[nccl-pg] print broadcast ncclunique id duration (#123963)

Summary: Print NCCL PG broadcast nccl unique id duration for measurement.

Differential Revision: D56048059

Pull Request resolved: https://github.com/pytorch/pytorch/pull/123963
Approved by: https://github.com/wconstab

caffe2/CMakeLists.txt

@@ -1732,7 +1732,7 @@ if(BUILD_TEST)
   foreach(test_src ${Caffe2_CPU_TEST_SRCS})
     get_filename_component(test_name ${test_src} NAME_WE)
     add_executable(${test_name} "${test_src}")
-    target_link_libraries(${test_name} torch_library gtest_main)
+    target_link_libraries(${test_name} torch_library gtest_main stdc++)
     target_include_directories(${test_name} PRIVATE $<INSTALL_INTERFACE:include>)
     target_include_directories(${test_name} PRIVATE $<BUILD_INTERFACE:${CMAKE_BINARY_DIR}/include>)
     target_include_directories(${test_name} PRIVATE ${Caffe2_CPU_INCLUDE})

test/cpp/c10d/ProcessGroupNCCLErrorsTest.cpp

@@ -371,7 +371,8 @@ std::string readTraceFromFile(const std::string& filename, size_t size) {
 // Extend the nested class outside the parent class
 class TestDebugInfoWriter : public c10d::DebugInfoWriter {
  public:
-  TestDebugInfoWriter() : DebugInfoWriter(0) {}
+  TestDebugInfoWriter(std::string namePrefix)
+      : DebugInfoWriter(namePrefix, 0) {}
 
   void write(const std::string& ncclTrace) override {
     traces_.assign(ncclTrace.begin(), ncclTrace.end());
@@ -415,10 +416,12 @@ TEST_F(ProcessGroupNCCLErrorsTest, testNCCLErrorsNoHeartbeat) {
   // The storer here is very similar to the fallback storer.
   // The only difference is that we are storing traces also in memory for
   // validation.
+  std::string fileNamePrefix = c10d::getCvarString(
+      {"TORCH_NCCL_DEBUG_INFO_TEMP_FILE"}, "/tmp/nccl_trace_rank_");
   std::unique_ptr<TestDebugInfoWriter> wrterForTestPtr =
-      std::make_unique<TestDebugInfoWriter>();
+      std::make_unique<TestDebugInfoWriter>(fileNamePrefix);
   std::vector<uint8_t>& traces = wrterForTestPtr->getTraces();
-  pg.registerDebugInfoWriter(std::move(wrterForTestPtr));
+  c10d::DebugInfoWriter::registerWriter(std::move(wrterForTestPtr));
 
   // Normal collective case.
   auto work = pg.allreduce(tensors_);
@@ -449,6 +452,9 @@ TEST_F(ProcessGroupNCCLErrorsTest, testNCCLErrorsNoHeartbeat) {
 class ProcessGroupNCCLWatchdogTimeoutTest : public ProcessGroupNCCLErrorsTest {
  protected:
   void SetUp() override {
+    // TODO (kwen2501)
+    GTEST_SKIP() << "Skipping tests under ProcessGroupNCCLWatchdogTimeoutTest; "
+                 << "will rewrite them after refactoring Work queues.";
     ProcessGroupNCCLErrorsTest::SetUp();
     std::string timeInterval = std::to_string(heartBeatIntervalInSec);
     ASSERT_TRUE(setenv(c10d::TORCH_NCCL_BLOCKING_WAIT[0].c_str(), "1", 1) == 0);

test/distributed/checkpoint/test_state_dict_utils.py

@@ -4,9 +4,10 @@ import torch
 import torch.distributed as dist
 import torch.distributed._functional_collectives as funcol
 
-from torch.distributed._tensor import DTensor
-from torch.distributed._tensor.placement_types import Shard
-from torch.distributed.checkpoint._state_dict_utils import (
+from torch.distributed._state_dict_utils import (
+    _check_state_dict_similarity,
+    _copy_state_dict,
+    _create_cpu_state_dict,
     _gather_state_dict,
     _offload_state_dict_to_cpu,
 )
@@ -115,6 +116,58 @@ class TestStateDictUtils(DTensorTestBase):
         }
         self.assertEqual(state_dict, _gather_state_dict(dist_state_dict))
 
+    @skip_if_lt_x_gpu(2)
+    def test_create_cpu_state_dict(self):
+        device = torch.device("cuda")
+        buffer = io.BytesIO()
+        torch.save(torch.ones(10), buffer)
+        buffer.seek(0)
+        state_dict = {
+            "tensor1": torch.arange(10, device=device),
+            "tensor2": torch.ones(10, device=device),
+            "non_tensor_bytes_io": copy.deepcopy(buffer),
+            "non_tensor_bytes": buffer.read(),
+            "step": torch.tensor(7, dtype=torch.float),
+            "lr": 1.5,
+            "nested": {"list": [1, 2, 3, 4]},
+        }
+
+        def _verify(cpu_state_dict):
+            # Verify the correctness of _check_state_dict_similarity()
+            self.assertTrue(_check_state_dict_similarity(state_dict, cpu_state_dict))
+            tensor1 = cpu_state_dict["tensor1"]
+            cpu_state_dict["tensor1"] = torch.arange(11)
+            self.assertFalse(_check_state_dict_similarity(state_dict, cpu_state_dict))
+            cpu_state_dict["tensor1"] = tensor1
+
+            _copy_state_dict(state_dict, cpu_state_dict)
+
+            # Verify if _copy_state_dict works
+            for v in cpu_state_dict.values():
+                if isinstance(v, torch.Tensor):
+                    self.assertFalse(v.is_cuda)
+            self.assertEqual(cpu_state_dict["tensor1"], torch.arange(10))
+            self.assertEqual(cpu_state_dict["tensor2"], torch.ones(10))
+            buffer.seek(0)
+            cpu_state_dict["non_tensor_bytes_io"].seek(0)
+            self.assertEqual(
+                cpu_state_dict["non_tensor_bytes_io"].read(), buffer.read()
+            )
+            buffer.seek(0)
+            self.assertEqual(cpu_state_dict["non_tensor_bytes"], buffer.read())
+            self.assertEqual(cpu_state_dict["lr"], 1.5)
+            self.assertEqual(cpu_state_dict["step"], 7)
+            self.assertEqual(cpu_state_dict["nested"], {"list": [1, 2, 3, 4]})
+
+        cpu_state_dict = _create_cpu_state_dict(state_dict, pin_memory=True)
+        _verify(cpu_state_dict)
+        cpu_state_dict = _create_cpu_state_dict(state_dict, share_memory=True)
+        _verify(cpu_state_dict)
+        cpu_state_dict = _create_cpu_state_dict(
+            state_dict, share_memory=True, pin_memory=True
+        )
+        _verify(cpu_state_dict)
+
 
 if __name__ == "__main__":
     run_tests()

test/distributed/test_c10d_nccl.py

@@ -11,6 +11,7 @@ import tempfile
 import threading
 import pickle
 import time
+import json
 import warnings
 from contextlib import contextmanager
 from datetime import datetime, timedelta
@@ -1334,6 +1335,19 @@ class ProcessGroupNCCLTest(MultiProcessTestCase):
         self.assertEqual(tensor, original_tensor)
 
 
+    @requires_nccl()
+    @skip_but_pass_in_sandcastle_if(not TEST_MULTIGPU, "NCCL test requires 2+ GPUs")
+    def test_set_process_group_desc(self):
+        store = c10d.FileStore(self.file_name, self.world_size)
+        device = torch.device(f'cuda:{self.rank}')
+        pg_default = self._create_process_group_nccl(store, self.opts(), device_id=device)
+        self.assertEqual(pg_default.group_desc, "default_pg")
+        pg_1 = c10d.new_group([0, 1], group_desc="test_purpose")
+        self.assertEqual(pg_1.group_desc, "test_purpose")
+        pg_2 = c10d.new_group([0, 1])
+        self.assertEqual(pg_2.group_desc, "undefined")
+
+
 class DistributedDataParallelTest(
     test_c10d_common.CommonDistributedDataParallelTest, MultiProcessTestCase
 ):
@@ -3542,11 +3556,12 @@ class SparseCollective(MultiProcessTestCase):
 class NCCLTraceTestBase(MultiProcessTestCase):
     def setUp(self):
         super().setUp()
-        os.environ["TORCH_NCCL_ENABLE_TIMING"] = '0'
+        os.environ["TORCH_NCCL_ENABLE_TIMING"] = '0'  # see 'timing_enabled' parametrized tests
         os.environ["TORCH_NCCL_TRACE_BUFFER_SIZE"] = '10'
         os.environ["TORCH_NCCL_DUMP_ON_TIMEOUT"] = '1'
         self.tempdir = tempfile.TemporaryDirectory()
         os.environ["TORCH_NCCL_DEBUG_INFO_TEMP_FILE"] = self._trace_basename()
+        os.environ["TORCH_NCCL_DEBUG_INFO_PIPE_FILE"] = self._trace_basename()
         self._spawn_processes()
 
     @classmethod
@@ -3617,28 +3632,50 @@ class NCCLTraceTest(NCCLTraceTestBase):
 
     @requires_nccl()
     @skip_but_pass_in_sandcastle_if(torch.cuda.device_count() < 2, "NCCL test requires 2+ GPUs")
-    def test_short(self):
+    @parametrize("timing_enabled", [True, False])
+    def test_short(self, timing_enabled):
         if self.rank == self.MAIN_PROCESS_RANK:
             return
         pg = self._create_process_group_nccl()
+        if timing_enabled:
+            pg._enable_collectives_timing()
         device = self.local_device
         a = torch.full((3, 4), float(self.rank), device=device)
         for i in range(2):
             f = pg.allreduce(a)
         f.wait()
         torch.cuda.synchronize(device=device)
+
+        # gah ok so now the duration_ms is populated best-effort since it can only happen outside "dump()" api
+        time.sleep(1)
+
         t = pickle.loads(torch._C._distributed_c10d._dump_nccl_trace())
+        ver = t['version']
+        self.assertEqual(ver, "1.1")
+        t = t['entries']
         self.assertEqual(len(t), 2)
         last = t[-1]
+        self.assertEqual(last['process_group'], ('0', 'default_pg'))
         self.assertEqual(last['state'], 'completed')
+        s = last['time_discovered_started_ns']
+        f = last['time_discovered_completed_ns']
+        self.assertIsNotNone(f)
+        if timing_enabled:
+            self.assertIsNotNone(s)
+            self.assertTrue(s <= f)
         self.assertIn('test_c10d_nccl.py', str(last['frames']))
         self.assertEqual(last['input_sizes'], ((3, 4),))
         self.assertEqual(last['output_sizes'], ((3, 4),))
         self.assertEqual(last['seq_id'], 2)
         now = datetime.now()
-        event_created_time = datetime.fromtimestamp(last['time_created_us'] / 1000000)
+        event_created_time = datetime.fromtimestamp(last['time_created_ns'] / 1000000000)
         before_test = now - timedelta(minutes=1)
         self.assertTrue(before_test < event_created_time < now)
+        if timing_enabled:
+            # very loose bounds, measured 0.036 ms on devgpu
+            self.assertTrue(0 < last['duration_ms'] < 100)
+        else:
+            self.assertTrue("duration_ms" not in last)
 
     @requires_nccl()
     @skip_but_pass_in_sandcastle_if(torch.cuda.device_count() < 2, "NCCL test requires 2+ GPUs")
@@ -3698,9 +3735,11 @@ class NCCLTraceTest(NCCLTraceTestBase):
         f.wait()
         torch.cuda.synchronize(device=device)
         t = pickle.loads(torch._C._distributed_c10d._dump_nccl_trace())
+        t = t['entries']
         self.assertEqual(len(t), 10)
         first = t[0]
         last = t[-1]
+        self.assertEqual(last['profiling_name'], 'nccl:all_reduce')
         self.assertEqual(last['state'], 'completed')
         self.assertIn('test_c10d_nccl.py', str(last['frames']))
         self.assertEqual(last['input_sizes'], ((3, 4),))
@@ -3732,6 +3771,8 @@ class NCCLTraceTest(NCCLTraceTestBase):
                 pg.allreduce(a).wait()
             e.synchronize()
             t = pickle.loads(torch._C._distributed_c10d._dump_nccl_trace())
+            t = t['entries']
+            self.assertEqual(t[-1]['profiling_name'], 'nccl:all_reduce')
             if self.rank == 0:
                 self.assertEqual(t[-1]['seq_id'], 1)
                 self.assertEqual(t[-1]['state'], 'completed')
@@ -3773,12 +3814,15 @@ class NCCLTraceTest(NCCLTraceTestBase):
                 # give the other thread some time to fill the cuda buffer
                 time.sleep(5)
                 t = pickle.loads(torch._C._distributed_c10d._dump_nccl_trace())
+                t = t['entries']
+                self.assertEqual(t[-1]['profiling_name'], 'nccl:all_reduce')
                 if self.rank == 0:
                     self.assertEqual(t[-1]['seq_id'], 1)
                     self.assertEqual(t[-1]['state'], 'completed')
                 else:
                     self.assertEqual(t[-1]['seq_id'], 2)
                     self.assertEqual(t[-1]['state'], self.started_or_scheduled(timing_enabled))
+                    self.assertIsNone(t[-1]['time_discovered_completed_ns'])
                 # this will eventually cause the missing rank 0
                 # to continue which will unblock the non-zero ranks
                 self.parent.send('next')
@@ -3832,6 +3876,10 @@ class NCCLTraceTestDumpOnTimeout(NCCLTraceTestDumpOnTimeoutBase):
     @skip_but_pass_in_sandcastle_if(torch.cuda.device_count() < 2, "NCCL test requires 2+ GPUs")
     @parametrize("timing_enabled", [True, False])
     def test_timeout_dumps(self, timing_enabled):
+        # dump on heartbeatmonitor thread
+        os.environ['TORCH_NCCL_COORD_CHECK_MILSEC'] = '1000'
+        # need rank0 to crash before looking for its output file
+        os.environ['TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC'] = '1'
 
         if self.rank == self.MAIN_PROCESS_RANK:
             # wait for rank0 to crash before looking for its output file
@@ -3839,6 +3887,7 @@ class NCCLTraceTestDumpOnTimeout(NCCLTraceTestDumpOnTimeoutBase):
             self.assertEqual(self._wait_process(0, timeout=90), -6)
             with open(self._trace_name(rank=0), 'rb') as f:
                 t = pickle.load(f)
+                t = t['entries']
                 self.assertEqual(len(t), 2)
                 self.assertEqual(t[0]['seq_id'], 1)
                 self.assertEqual(t[0]['state'], 'completed')
@@ -3868,7 +3917,7 @@ class NCCLTraceTestDumpOnTimeout(NCCLTraceTestDumpOnTimeoutBase):
 instantiate_parametrized_tests(NCCLTraceTestDumpOnTimeout)
 instantiate_parametrized_tests(NCCLTraceTest)
 
-class NCCLTraceTestTimeoutDumpOnIdleRanks(NCCLTraceTestDumpOnTimeoutBase):
+class NCCLTraceTestTimeoutDumpOnStuckRanks(NCCLTraceTestDumpOnTimeoutBase):
     def _check_return_codes(self, elapsed_time):
         # the base test infra assumes processes exit with matching return codes,
         # but we want rank0 to abort and rank1 to exit cleanly in this test
@@ -3877,7 +3926,7 @@ class NCCLTraceTestTimeoutDumpOnIdleRanks(NCCLTraceTestDumpOnTimeoutBase):
 
     @requires_nccl()
     @skip_but_pass_in_sandcastle_if(torch.cuda.device_count() < 2, "NCCL test requires 2+ GPUs")
-    def test_timeout_dumps_on_idle_ranks(self):
+    def test_timeout_dumps_on_stuck_ranks(self):
 
         if self.rank == self.MAIN_PROCESS_RANK:
             # wait for both rank0 and 1 to crash before looking for both ranks' output
@@ -3888,20 +3937,17 @@ class NCCLTraceTestTimeoutDumpOnIdleRanks(NCCLTraceTestDumpOnTimeoutBase):
             self.assertTrue(os.path.exists(self._trace_name(rank=0)))
             with open(self._trace_name(rank=0), 'rb') as f:
                 t = pickle.load(f)
+                t = t['entries']
                 self.assertEqual(len(t), 2)
             with open(self._trace_name(rank=1), 'rb') as f:
                 t = pickle.load(f)
+                t = t['entries']
                 self.assertEqual(len(t), 1)
                 self.assertEqual(t[0]['seq_id'], 1)
                 self.assertEqual(t[0]['state'], 'completed')
             return
 
-        # Set heartbeat timeout to a shorter one (default timeout is 2 min).
-        os.environ[
-            "TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC"
-        ] = f"{NCCLTraceTestDumpOnTimeoutBase.timeout_sec * 2}"
         pg = self._create_process_group_nccl()
-
         device = self.local_device
         with torch.cuda.device(device):
             a = torch.full((3, 4), float(self.rank), device=device)
@@ -3910,12 +3956,68 @@ class NCCLTraceTestTimeoutDumpOnIdleRanks(NCCLTraceTestDumpOnTimeoutBase):
             if self.rank == 0:
                 pg.allreduce(a).wait()
 
-            # rank 0 will crash before it passes the sync, but rank1 will exit quickly and cleanly
+            # rank 0 will get stuck, timeout and then signal a timeout to all ranks.
             torch.cuda.synchronize()
 
-            # Force rank 1 to idle so that it also gets debug info dump triggered.
             if self.rank == 1:
-                time.sleep(6)
+                # Force rank 1 to idle so that it will eventually timeout as well after
+                # getting the global signal to dump the debugging info.
+                time.sleep(600)
+
+class NcclErrorDumpTest(NCCLTraceTestBase):
+    def _wait_process(self, rank, timeout):
+        try:
+            self.processes[rank].join(timeout)
+            return self.processes[rank].exitcode
+        except TimeoutError:
+            return None
+
+    def _check_return_codes(self, elapsed_time):
+        # the base test infra assumes processes exit with matching return codes,
+        # but we want rank0 to abort with exception and rank1 to exit with exit 1
+        self.assertEqual(self.processes[0].exitcode, -6)
+        self.assertEqual(self.processes[1].exitcode, 1)
+
+    @requires_nccl()
+    @requires_nccl_version((2, 4, 0), "Need NCCL 2.4+ for error checking")
+    @skip_if_lt_x_gpu(2)
+    @skip_if_rocm
+    def test_nccl_errors_dump(self):
+        os.environ["TORCH_NCCL_ASYNC_ERROR_HANDLING"] = "1"
+        os.environ["TORCH_NCCL_TRACE_BUFFER_SIZE"] = '1000'
+        os.environ["TORCH_NCCL_DUMP_ON_TIMEOUT"] = '1'
+        # need rank0 to dump before abort
+        os.environ['TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC'] = '5'
+
+        if self.rank == self.MAIN_PROCESS_RANK:
+            # wait for both rank0 and 1 to crash before looking for dump
+            self.assertEqual(self._wait_process(0, timeout=90), -6)
+            self.assertEqual(self._wait_process(1, timeout=90), 1)
+            # verify that the trace file exists for rank0
+            self.assertTrue(os.path.exists(self._trace_name(rank=0)))
+            return
+
+        store = c10d.FileStore(self.file_name, self.world_size)
+        process_group = c10d.ProcessGroupNCCL(
+            store,
+            self.rank,
+            self.world_size,
+            timeout=timedelta(seconds=10),
+        )
+        process_group.allreduce(torch.rand(10).cuda(self.rank))
+        if self.rank == 0:
+            work = process_group.allreduce(torch.rand(10).cuda(self.rank))
+            # expect an error to be raised
+            with self.assertRaisesRegex(dist.DistBackendError, ""):
+                # Block the current stream on the NCCL stream
+                work.wait()
+                # Run some GPU operations
+                a = torch.rand(10).cuda(self.rank)
+        elif self.rank == 1:
+            # Clean up structures (ex: files for FileStore before going down)
+            del process_group
+            sys.exit(1)
+
 
 if __name__ == "__main__":
     assert (

test/distributed/test_store.py

@@ -71,7 +71,7 @@ class StoreTestBase:
     def _create_store(self, i):
         raise RuntimeError("not implemented")
 
-    def _test_set_get(self, fs):
+    def _test_set_get_check(self, fs):
         fs.add("key", 1)
         fs.add("key", 2)
         fs.add("key", 3)
@@ -90,14 +90,16 @@ class StoreTestBase:
         self.assertEqual(b"value1", fs.get("key1"))
         self.assertEqual(b"value2", fs.get("key2"))
         self.assertEqual(b"21", fs.get("key3"))
+        self.assertTrue(fs.check(["key3"]))
+        self.assertFalse(fs.check(["Randomkey3"]))
 
         fs.set("-key3", "7")
         self.assertEqual(b"7", fs.get("-key3"))
         fs.delete_key("-key3")
         self.assertEqual(fs.num_keys(), self.num_keys_total)
 
-    def test_set_get(self):
-        self._test_set_get(self._create_store())
+    def test_set_get_check(self):
+        self._test_set_get_check(self._create_store())
 
     def _test_compare_set(self, store):
         missing_key_result = store.compare_set("cs_key0", "wrong_old_value", "new_value0")
@@ -441,6 +443,12 @@ class PrefixTCPStoreTest(TestCase, StoreTestBase):
     def num_keys_total(self):
         return 6
 
+    def test_underlying_non_prefix_store(self):
+        store = self._create_store()
+        wrapped_store = dist.PrefixStore(self.prefix, dist.PrefixStore(self.prefix, store))
+        self.assertEqual(self.tcpstore, store._underlying_non_prefix_store)
+        self.assertEqual(self.tcpstore, wrapped_store._underlying_non_prefix_store)
+
 class MyPythonStore(dist.Store):
     def __init__(self):
         super().__init__()

torch/_C/_distributed_c10d.pyi

@@ -463,6 +463,7 @@ class ProcessGroup:
         backend: Optional[ProcessGroup],
     ) -> None: ...
     def _set_group_name(self, name: str) -> None: ...
+    def _set_group_desc(self, desc: str) -> None: ...
     def name(self) -> str: ...
     def _has_hooks(self) -> bool: ...
     def _wait_for_pending_works(self) -> None: ...
@@ -471,6 +472,10 @@ class ProcessGroup:
     def bound_device_id(self) -> Optional[torch.device]: ...
     @bound_device_id.setter
     def bound_device_id(self, device: Optional[torch.device]) -> None: ...
+    @property
+    def group_name(self) -> str: ...
+    @property
+    def group_desc(self) -> str: ...
 
 class ProcessGroupRoundRobin(ProcessGroup): ...
 

torch/csrc/distributed/c10d/Backend.hpp

@@ -369,6 +369,14 @@ class TORCH_API Backend : public torch::CustomClassHolder {
     return pg_name_;
   }
 
+  void setGroupDesc(const std::string& desc) {
+    pg_desc_ = desc;
+  }
+
+  const std::string& getGroupDesc() const {
+    return pg_desc_;
+  }
+
   // See similar functions in ProcessGroup.hpp for context.
   c10::optional<at::Device> getBoundDeviceId() const {
     return bound_device_id_;
@@ -399,6 +407,7 @@ class TORCH_API Backend : public torch::CustomClassHolder {
   // remains the same across use of this process group.
   DebugLevel dist_debug_level_;
   std::string pg_name_;
+  std::string pg_desc_;
 
   std::function<void(std::shared_ptr<WorkInfo>)> onCompletionHook_;
 

torch/csrc/distributed/c10d/NCCLUtils.hpp

@@ -8,6 +8,7 @@
 #include <memory>
 #include <mutex>
 
+#include <ATen/ATen.h>
 #include <c10/util/Exception.h>
 #include <c10/util/Optional.h>
 #include <nccl.h>
@@ -175,14 +176,29 @@ std::string getNcclErrorDetailStr(
     c10::optional<std::string> processGroupFailureReason = c10::nullopt);
 
 // Write NCCL debug info to local disk or any storage users define.
+// There are some constrains we set for the debug info writer:
+// 1. The writer should only be registered once.
+// 2. Once registered, users cannot change it including un-register.
+// 3. It is recommended to register the customized writer in the trainer setup,
+//    If users don't register before calling launchAsyncDebugDump, then users
+//    lose the chance to register (and the default writer will be
+//    auto-registered).
 class TORCH_API DebugInfoWriter {
  public:
-  DebugInfoWriter(int rank);
   virtual ~DebugInfoWriter();
   virtual void write(const std::string& ncclTrace);
+  static DebugInfoWriter& getWriter(int rank);
+  static void registerWriter(std::unique_ptr<DebugInfoWriter> writer);
 
  protected:
+  DebugInfoWriter(std::string namePrefix, int rank) {
+    filename_ = c10::str(namePrefix, rank);
+  }
   std::string filename_;
+
+ private:
+  static std::unique_ptr<DebugInfoWriter> writer_;
+  static std::atomic<bool> hasWriterRegistered_;
 };
 
 // RAII wrapper for NCCL communicator
@@ -267,6 +283,18 @@ class NCCLComm {
   }
 #endif
 
+#if defined(IS_NCCL_EXP) && defined(NCCL_COMM_DUMP)
+  std::unordered_map<std::string, std::string> ncclCommDump() {
+    std::unordered_map<std::string, std::string> dump;
+    if (isAborted()) {
+      LOG(INFO) << "Communicator was aborted before trying to dump its state.";
+      return dump;
+    }
+    C10D_NCCL_CHECK(::ncclCommDump(ncclComm_, dump), c10::nullopt);
+    return dump;
+  }
+#endif
+
   ncclUniqueId getNcclId() {
     return ncclId_;
   }
@@ -322,6 +350,9 @@ class NCCLComm {
     // Set true failure reason if provided by ProcessGroupNCCL (e.g. work
     // timeout)
     commFailureReason_ = commFailureReason;
+    LOG(INFO) << "Aborting ncclComm_ " << ncclComm_ << " with reason: "
+              << (commFailureReason ? *commFailureReason
+                                    : "No abort reason provided.");
 #ifndef NCCL_HAS_COMM_NONBLOCKING
     C10D_NCCL_CHECK(::ncclCommAbort(ncclComm_), commFailureReason_);
 #else
@@ -421,6 +452,8 @@ class NCCLComm {
 #endif
   }
 
+  friend class ProcessGroupNCCL;
+
  protected:
   ncclComm_t ncclComm_;
   // Unique nccl_id for this communicator.

torch/csrc/distributed/c10d/PrefixStore.cpp

@@ -108,4 +108,22 @@ c10::intrusive_ptr<Store> PrefixStore::getUnderlyingStore() {
   return store_;
 }
 
+c10::intrusive_ptr<Store> PrefixStore::getUnderlyingNonPrefixStore() {
+  c10::intrusive_ptr<Store> store = store_;
+
+  while (store) {
+    // Attempt to dynamically cast to PrefixStore
+    PrefixStore* asPrefixStore = dynamic_cast<PrefixStore*>(store.get());
+    if (asPrefixStore) {
+      store = asPrefixStore->getUnderlyingStore();
+    } else {
+      break; // We've reached a non-PrefixStore
+    }
+  }
+
+  TORCH_CHECK(
+      store != nullptr, "Underlying Non-PrefixStore shouldn't be null.");
+  return store;
+}
+
 } // namespace c10d

torch/csrc/distributed/c10d/PrefixStore.hpp

@@ -53,6 +53,9 @@ class TORCH_API PrefixStore : public Store {
 
   c10::intrusive_ptr<Store> getUnderlyingStore();
 
+  // Recursively to fetch the store before layers of wrapping with PrefixStore.
+  c10::intrusive_ptr<Store> getUnderlyingNonPrefixStore();
+
  protected:
   std::string prefix_;
   c10::intrusive_ptr<Store> store_;

torch/csrc/distributed/c10d/ProcessGroup.cpp

@@ -165,6 +165,18 @@ void ProcessGroup::setGroupName(const std::string& name) {
   }
 }
 
+const std::string& ProcessGroup::getGroupDesc() const {
+  return pg_desc_;
+}
+
+void ProcessGroup::setGroupDesc(const std::string& name) {
+  pg_desc_ = name;
+  // Also set the group desc for all backends
+  for (auto& kv : deviceTypeToBackend_) {
+    kv.second->setGroupDesc(name);
+  }
+}
+
 void ProcessGroup::enableCollectivesTiming() {
   for (auto& kv : deviceTypeToBackend_) {
     kv.second->enableCollectivesTiming();

torch/csrc/distributed/c10d/ProcessGroup.hpp

@@ -694,6 +694,8 @@ class TORCH_API ProcessGroup : public torch::CustomClassHolder {
 
   const std::string& getGroupName() const;
   void setGroupName(const std::string& name);
+  const std::string& getGroupDesc() const;
+  void setGroupDesc(const std::string& name);
   void enableCollectivesTiming();
 
   void release_resources() override;
@@ -724,6 +726,7 @@ class TORCH_API ProcessGroup : public torch::CustomClassHolder {
   const int size_;
   const c10::intrusive_ptr<Options> options_;
   const BackendType backendType_;
+  std::string pg_desc_;
 
   // Debug level setting. It is parsed once when ProcessGroup is constructed and
   // remains the same across use of this process group.

torch/csrc/distributed/c10d/ProcessGroupNCCL.hpp

@@ -1,7 +1,15 @@
 #pragma once
 
+#if defined(__linux__)
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
 #ifdef USE_C10D_NCCL
 
+#include <atomic>
 #include <chrono>
 #include <future>
 #include <iostream>
@@ -12,6 +20,7 @@
 
 #include <torch/csrc/distributed/c10d/Backend.hpp>
 #include <torch/csrc/distributed/c10d/NCCLUtils.hpp>
+#include <torch/csrc/distributed/c10d/PrefixStore.hpp>
 #include <torch/csrc/distributed/c10d/Store.hpp>
 
 #include <ATen/DynamicLibrary.h>
@@ -26,52 +35,74 @@
 #include <torch/custom_class.h>
 
 namespace c10d {
-// Environment variable which controls whether we perform a NCCL healt check
+// Control whether we perform a NCCL health check or not
 // which ensures communicators are healthy at the beginning of init.
 static std::vector<std::string> TORCH_ENABLE_NCCL_HEALTH_CHECK = {
     "TORCH_ENABLE_NCCL_HEALTH_CHECK",
     "ENABLE_NCCL_HEALTH_CHECK"};
 
-// Environment variable which controls whether or not wait() is blocking or
-// non-blocking.
+// Control whether or not wait() is blocking or non-blocking.
 static std::vector<std::string> TORCH_NCCL_BLOCKING_WAIT = {
     "TORCH_NCCL_BLOCKING_WAIT",
     "NCCL_BLOCKING_WAIT"};
 
-// Environment variable which controls whether or not we perform Async Error
-// Handling with NCCL.
+// Control whether or not we perform Async Error Handling with NCCL.
 static std::vector<std::string> TORCH_NCCL_ASYNC_ERROR_HANDLING = {
     "TORCH_NCCL_ASYNC_ERROR_HANDLING",
     "NCCL_ASYNC_ERROR_HANDLING"};
 
-// Environment Variable to control whether dumping debug info on watchdog
+// Control whether dumping debug info on watchdog
 // timeout is enabled. This variable must be set together with
 // TORCH_NCCL_ENABLE_MONITORING=1 and TORCH_NCCL_TRACE_BUFFER_SIZE > 0.
 static std::vector<std::string> TORCH_NCCL_DUMP_ON_TIMEOUT = {
     "TORCH_NCCL_DUMP_ON_TIMEOUT"};
 
-// Environment Variable to control whether Desync Debug is enabled.
-// This variable must be set together with TORCH_NCCL_ASYNC_ERROR_HANDLING.
+// Control whether Desync Debug is enabled. This variable must be set
+// together with TORCH_NCCL_ASYNC_ERROR_HANDLING.
 static std::vector<std::string> TORCH_NCCL_DESYNC_DEBUG = {
     "TORCH_NCCL_DESYNC_DEBUG",
     "NCCL_DESYNC_DEBUG"};
 
+// Enable recording start-events for all ProcessGroupNCCL collectives, and
+// compute accurate collective timing per-collective. (Note: end-events are
+// recorded by default. Turn on this flag can increase chances of a watchdog
+// hang due to performing a CUDA event query which eventually calls
+// cudaEventElapsedTime() API.
 static std::vector<std::string> TORCH_NCCL_ENABLE_TIMING = {
     "TORCH_NCCL_ENABLE_TIMING",
     "NCCL_ENABLE_TIMING"};
 
+// Enable monitoring thread which aborts the process when the ProcessGroupNCCL
+// Watchdog thread gets stuck and no heartbeat is detected after
+// TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC. This can happen due to calling CUDA/NCCL
+// APIs that may hang. It is Useful to prevent jobs being stuck for a prolonged
+// time than necessary tying up cluster resources.
 static std::vector<std::string> TORCH_NCCL_ENABLE_MONITORING = {
     "TORCH_NCCL_ENABLE_MONITORING"};
 
+// Control the watchdog heartbeat timeout period after which the monitoring
+// thread will abort the process.
 static std::vector<std::string> TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC = {
     "TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC"};
 
+// The maximum number of events we store in the flight recorder's ring buffer.
+// (One event could be the start or end of a collective, for example).
 static std::vector<std::string> TORCH_NCCL_TRACE_BUFFER_SIZE = {
     "TORCH_NCCL_TRACE_BUFFER_SIZE"};
 
+// Control how much extra time we will wait for dumping the debugging info
+// before we exit and throws timeout exception.
+static std::vector<std::string> TORCH_NCCL_WAIT_TIMEOUT_DUMP_MILSEC = {
+    "TORCH_NCCL_WAIT_TIMEOUT_DUMP_MILSEC"};
+
+// Control the interval inside the watchdog thread to check the coordinated
+// signal from other ranks, e.g. to dump the debugging information.
+static std::vector<std::string> TORCH_NCCL_COORD_CHECK_MILSEC = {
+    "TORCH_NCCL_COORD_CHECK_MILSEC"};
+
 constexpr const char* NCCL_BACKEND_NAME = "nccl";
 
-constexpr const char* TIMEOUT_DUMP = "timeout_dump";
+constexpr const char* EXCEPTION_DUMP = "exception_dump";
 
 constexpr auto kProcessGroupNCCLDefaultTimeout =
     std::chrono::milliseconds(10 * 60 * 1000);
@@ -110,6 +141,59 @@ static std::vector<std::string> TORCH_NCCL_USE_TENSOR_REGISTER_ALLOCATOR_HOOK =
     {"TORCH_NCCL_USE_TENSOR_REGISTER_ALLOCATOR_HOOK",
      "NCCL_USE_TENSOR_REGISTER_ALLOCATOR_HOOK"};
 
+#if defined(__linux__)
+struct DumpPipe {
+  DumpPipe(int rank) {
+    std::string fileStem =
+        getCvarString({"TORCH_NCCL_DEBUG_INFO_PIPE_FILE"}, "");
+    if (fileStem.empty() ||
+        getCvarInt({"TORCH_NCCL_TRACE_BUFFER_SIZE"}, 0) <= 0) {
+      return;
+    }
+    TORCH_CHECK(!fileStem.empty(), "TORCH_NCCL_DEBUG_INFO_TEMP_FILE is empty");
+    std::string filename = c10::str(fileStem, rank, ".pipe");
+    TORCH_CHECK(
+        unlink(filename.c_str()) != -1 || errno == ENOENT,
+        "Error removing existing named pipe ",
+        filename);
+    TORCH_CHECK(
+        mkfifo(filename.c_str(), 0666) != -1,
+        "Error creating named pipe ",
+        filename);
+    fd_ = open(filename.c_str(), O_RDONLY | O_NONBLOCK);
+    LOG(INFO) << "Pipe file " << filename
+              << " has been opened, write to it to trigger NCCL Debug Dump.";
+    TORCH_CHECK(fd_ != -1, "Error opening named pipe ", filename);
+  }
+  bool shouldDump() {
+    if (fd_ == -1) {
+      return false;
+    }
+    char buf[128];
+    // non-blocking from O_NONBLOCK above.
+    // Ignore EINTR because we already will poll this
+    // again later.
+    ssize_t bytesRead = read(fd_, &buf, 128);
+    return bytesRead > 0;
+  }
+  ~DumpPipe() {
+    if (fd_ != -1) {
+      close(fd_);
+    }
+  }
+
+ private:
+  int fd_ = -1;
+};
+#else
+struct DumpPipe {
+  DumpPipe(int rank) {}
+  bool shouldDump() {
+    return false;
+  }
+};
+#endif
+
 // ProcessGroupNCCL implements NCCL bindings for c10d.
 //
 // All functions of the class are expected to be called in the same order
@@ -205,6 +289,8 @@ class TORCH_API ProcessGroupNCCL : public Backend {
 
     uint64_t getSequencenumber() const override;
 
+    const std::string& logPrefix() const;
+
     // Helper function that sets an exception_ptr on the WorkNCCL object.
     void setException(std::exception_ptr exception_ptr);
 
@@ -358,6 +444,7 @@ class TORCH_API ProcessGroupNCCL : public Backend {
     // via `ncclCommSplit`
     std::shared_ptr<ProcessGroupNCCL> split_from;
     int64_t split_color{0};
+    std::string group_name;
   };
 
   // If you wish to create multiple process groups, each with a potentially
@@ -540,8 +627,11 @@ class TORCH_API ProcessGroupNCCL : public Backend {
 
   void enableCollectivesTiming() override;
 
-  // Provide an API for users to define their own ways to store NCCL debug info.
-  void registerDebugInfoWriter(std::unique_ptr<DebugInfoWriter> writer);
+  // Helper function for iteratively aborting communicators in the provided map
+  void abortCommsFromMap(
+      std::unordered_map<std::string, std::vector<std::shared_ptr<NCCLComm>>>&
+          ncclCommsMap,
+      c10::optional<std::string> abortReason);
 
   // Provides an API to abort the ProcessGroup (similar to ncclCommAbort)
   // instead of relying on ProcessGroupNCCL destructor.
@@ -694,6 +784,19 @@ class TORCH_API ProcessGroupNCCL : public Backend {
   // Desync debug helper
   void logWorkEnd(WorkNCCL& work);
 
+  // Generates a prefix that is unique to this process group and rank, for
+  // disambiguating logs
+  std::string createLogPrefix() const;
+
+  // Returns the unique prefix created in createLogPrefix
+  const std::string& logPrefix() const;
+
+  // Returns the global rank of the device. This function assumes that users
+  // always create a default global process group(PG) which includes all
+  // devices. It is called in the constructor of ProcessGroupNCCL, so it always
+  // return the rank_ of the the very first PG created, aka, default global PG.
+  const int& globalRank() const;
+
  protected:
   // Function that runs as part of a separate thread aside from watchdog
   // thread because we need to check the heartbeat from watchdog thread
@@ -712,6 +815,19 @@ class TORCH_API ProcessGroupNCCL : public Backend {
   // for dump completion.
   std::future<bool> launchAsyncDebugDump();
 
+  // Helper to wait up to the specified timeout and then abandon the dump.
+  // Logs on timeout, and asserts the future's status is as expected.
+  void waitForDumpOrTimeout(
+      std::future<bool>& fut,
+      const std::chrono::time_point<std::chrono::steady_clock>& wakeUpTime,
+      size_t timeout_sec = 30);
+
+  // A helper function to wait for a future to complete or timeout.
+  void waitForFutureOrTimeout(
+      std::future<bool>& fut,
+      const std::chrono::milliseconds& timeOutMilSec,
+      const std::string& futDescription);
+
   // When watchdog timeout, this function will be called and return debug info
   // for users. For now we only get information from retrieveDesyncReport.
   // We are working on enabling more useful debug information for watchdog
@@ -720,9 +836,16 @@ class TORCH_API ProcessGroupNCCL : public Backend {
 
   static const int64_t kWatchdogThreadSleepMillis;
 
-  // The store is used to broadcast the NCCL unique ID of rank 0.
+  // The store is used to broadcast the NCCL unique ID of rank 0. This store
+  // comes with prefix and it is different across ProcessGroup NCCL instances
+  // (aka, different ProcessGroups).
   c10::intrusive_ptr<Store> store_;
 
+  // Reference to the store without prefix so that keys are same across all
+  // ProcessGroup NCCL instances and (key, value) pairs written to the store are
+  // global.
+  c10::intrusive_ptr<Store> globalStore_;
+
   bool storeError_{false};
 
   const c10::intrusive_ptr<Options> options_;
@@ -781,11 +904,18 @@ class TORCH_API ProcessGroupNCCL : public Backend {
   std::mutex mutex_;
 
   // Heartbeat of watchdog thread.
-  uint64_t heartbeat_;
+  std::atomic_uint64_t heartbeat_;
 
   // The time interval used for deciding whether there is no watchdog heartbeat.
   int heartbeatTimeoutInSec_;
 
+  // Extra time of sleep when waiting for timeout dump to finish.
+  int waitTimeoutDumpInMilSec_;
+
+  // Interval of check coordinated signals in ProcessGroupNCCL from other ranks
+  // e.g., trigger the dump of the debugging info for timeout when notified.
+  int coordCheckIntervalMilSec_;
+
   // Size of ring buffer where we store NCCL Traces for debugging.
   int ncclTraceBufferSize_;
 
@@ -815,6 +945,15 @@ class TORCH_API ProcessGroupNCCL : public Backend {
   // Whether there are hooks pending to be fired
   std::atomic<bool> hasPendingHooks_;
 
+  // This is the signal from watchdog threads to indicate whether the monitor
+  // thread should dump. Making it static so that it is accessiable from all the
+  // PGs. With this flag, monitor thread would dump debug info under any one of
+  // the 3 conditions: 1: this flag is set to true by the watchdog thread when
+  // it detects a timeout. 2: timeout signal is received from
+  // other ranks through tcpstore 3: no heartbeat of watchdog Note that only the
+  // monitor thread from PG0 should dump the debug info and only once
+  static std::atomic<bool> shouldDump_;
+
   // Mutex to Guard workMetaList_
   std::mutex workMetaListMutex_;
 
@@ -823,9 +962,6 @@ class TORCH_API ProcessGroupNCCL : public Backend {
 
   bool writeDebugInfo_ = false;
 
-  // Mutex to Guard the check of writeDebugInfo_
-  std::mutex writeDebugInfoMutex_;
-
   // Condition Variable for watchdog thread sleep
   std::condition_variable workMetaListCV_;
 
@@ -902,8 +1038,9 @@ class TORCH_API ProcessGroupNCCL : public Backend {
   // Whether or not to enable timeout root cause analysis.
   bool desyncDebug_;
 
-  // Whether or not to dump debug info on timeout
-  bool dumpOnTimeout_;
+  // Whether or not to dump debug info on exception including both watchdog
+  // timeout and nccl errors.
+  bool dumpOnException_;
 
   // Whether or not to create start CUDAEvent and enable timing for start
   // and end events. Note that enableTiming_ is always true if desyncDebug_
@@ -929,14 +1066,25 @@ class TORCH_API ProcessGroupNCCL : public Backend {
 
   std::exception_ptr watchDogException_ = nullptr;
 
-  // The callback function to store NCCL debug info.
-  std::unique_ptr<DebugInfoWriter> debugInfoWriter_ = nullptr;
-
   size_t uid_;
+
+  std::string logPrefix_;
 };
 
 TORCH_API std::string dump_nccl_trace();
 
+// Gets a mutable reference to a global optional function.  Heartbeat Monitor
+// will query this function and if available, call it to dump traces. Inside
+// fbcode, we store a function here that uses an internal tool for process
+// tracing
+TORCH_API c10::optional<std::function<std::string()>>& get_cpp_trace_dumper();
+
+// Similar to get_cpp_trace_dumper, this stores a function defined in
+// torch-python layer that lets us check whether the GIL can be acquired,
+// helpful for instrumenting in cases where a hang was observed.
+typedef bool (*gil_checker_t)();
+
+TORCH_API gil_checker_t& get_gil_checker();
 } // namespace c10d
 
 #endif // USE_C10D_NCCL

torch/csrc/distributed/c10d/TraceUtils.h

@@ -13,7 +13,6 @@
 #include <string>
 #include <system_error>
 #include <vector>
-
 namespace c10d {
 
 /* Trace Utils Related to TORCH_NCCL_DESYNC_DEBUG */
@@ -269,10 +268,20 @@ inline std::string retrieveDesyncReport(
 
 #ifdef USE_C10D_NCCL
 
-DebugInfoWriter::DebugInfoWriter(int rank) {
-  std::string fileName = getCvarString(
-      {"TORCH_NCCL_DEBUG_INFO_TEMP_FILE"}, "/tmp/nccl_trace_rank_");
-  filename_ = c10::str(fileName, rank);
+/* Helper used by work::getDuration() and nccl flight recorder */
+float getDurationFromFirstEvent(
+    const std::vector<at::cuda::CUDAEvent>& ncclStartEvents,
+    const std::vector<at::cuda::CUDAEvent>& ncclEndEvents) {
+  TORCH_CHECK(
+      ncclStartEvents.size() == 1,
+      "getDuration only works for single device per ProcessGroup, but found multiple start events.");
+  TORCH_CHECK(
+      ncclEndEvents.size() == 1,
+      "getDuration only works for single device per ProcessGroup, but found multiple end events.");
+  TORCH_CHECK(
+      ncclEndEvents[0].query(),
+      "getDuration can only be called after work is succeeded.")
+  return ncclStartEvents[0].elapsed_time(ncclEndEvents[0]);
 }
 
 DebugInfoWriter::~DebugInfoWriter() = default;
@@ -293,6 +302,31 @@ void DebugInfoWriter::write(const std::string& ncclTrace) {
   LOG(INFO) << "Finished writing NCCLPG debug info to " << filename_;
 }
 
+DebugInfoWriter& DebugInfoWriter::getWriter(int rank) {
+  if (writer_ == nullptr) {
+    std::string fileNamePrefix = getCvarString(
+        {"TORCH_NCCL_DEBUG_INFO_TEMP_FILE"}, "/tmp/nccl_trace_rank_");
+    // Using std::unique_ptr here to auto-delete the writer object
+    // when the pointer itself is destroyed.
+    std::unique_ptr<DebugInfoWriter> writerPtr(
+        new DebugInfoWriter(fileNamePrefix, rank));
+    DebugInfoWriter::registerWriter(std::move(writerPtr));
+  }
+  return *writer_;
+}
+
+void DebugInfoWriter::registerWriter(std::unique_ptr<DebugInfoWriter> writer) {
+  TORCH_CHECK_WITH(
+      DistBackendError,
+      hasWriterRegistered_.load() == false,
+      "debugInfoWriter already registered");
+  hasWriterRegistered_.store(true);
+  writer_ = std::move(writer);
+}
+
+std::unique_ptr<DebugInfoWriter> DebugInfoWriter::writer_ = nullptr;
+std::atomic<bool> DebugInfoWriter::hasWriterRegistered_(false);
+
 inline std::string pickle_str(const c10::IValue& v) {
   std::vector<char> result;
   {
@@ -317,6 +351,18 @@ inline c10::List<c10::IValue> new_list() {
   return c10::List<c10::IValue>(c10::AnyType::get());
 }
 
+inline std::string ranks_str(const std::vector<uint64_t>& ranks) {
+  std::string str;
+  for (const auto& rank : ranks) {
+    if (str.empty()) {
+      str = std::to_string(rank);
+    } else {
+      str += ", " + std::to_string(rank);
+    }
+  }
+  return c10::str("[", str, "]");
+}
+
 struct NCCLTraceBuffer {
   static NCCLTraceBuffer* get() {
     // intentionally leak on exit
@@ -336,11 +382,12 @@ struct NCCLTraceBuffer {
                 // buffer this entry will be located to
                 // update state information
     size_t pg_id_;
+    std::string pg_name_;
     size_t seq_id_; // as tracked by the process group
-    const char* profiling_name_;
+    std::string profiling_name_;
 
     std::shared_ptr<torch::CapturedTraceback> traceback_;
-    // we borrow pointser to start_ and end_ so we can query the state
+    // we borrow pointers to start_ and end_ so we can query the state
     // on reporting. However, once the event is completed, the call
     // to `complete` will clear these.
     EventList *start_, *end_;
@@ -348,8 +395,18 @@ struct NCCLTraceBuffer {
     // timestamp when the entry was created, likely close to the time the work
     // was 'enqueued'- not necessarily started
     c10::time_t time_created_;
+    c10::optional<float> duration_;
 
-    const char* state_ = "scheduled";
+    // timestamp when our CPU threads discovered that the kernel started.
+    // will always be _after_ it actually started, and can be very late
+    // if the watchdog thread got stuck on CUDA APIs.
+    c10::optional<c10::time_t> time_discovered_started_;
+
+    // timestamp when our CPU threads discovered that the kernel completed.
+    // will always be _after_ it actually complated, and can be the same time
+    // as the discovery of the start if the watchdog thread is stuck on CUDA
+    // APIs
+    c10::optional<c10::time_t> time_discovered_completed_;
 
     // size information for input/output tensors
     c10::SmallVector<int, 4> input_dims_;
@@ -369,8 +426,9 @@ struct NCCLTraceBuffer {
 
   c10::optional<size_t> record(
       size_t pg_id,
+      const std::string& pg_name,
       size_t seq_id,
-      const char* profiling_name,
+      std::string profiling_name,
       const std::vector<at::Tensor>& inputs,
       const std::vector<at::Tensor>& outputs,
       EventList* start,
@@ -385,8 +443,9 @@ struct NCCLTraceBuffer {
     auto te = Entry{
         id_,
         pg_id,
+        pg_name,
         seq_id,
-        profiling_name,
+        std::move(profiling_name),
         std::move(traceback),
         std::move(start),
         std::move(end),
@@ -424,8 +483,8 @@ struct NCCLTraceBuffer {
           break;
         }
       }
-      if (started) {
-        r.state_ = "started";
+      if (started && !r.time_discovered_started_) {
+        r.time_discovered_started_ = c10::getTime();
       }
     }
     if (r.end_ != nullptr) {
@@ -436,8 +495,8 @@ struct NCCLTraceBuffer {
           break;
         }
       }
-      if (completed) {
-        r.state_ = "completed";
+      if (completed && !r.time_discovered_completed_) {
+        r.time_discovered_completed_ = c10::getTime();
       }
     }
   }
@@ -456,35 +515,97 @@ struct NCCLTraceBuffer {
     return result;
   }
 
-  void retire_id(c10::optional<size_t> id) {
+  /*
+  Mark an Event as completed and free its events.
+
+  This is called by the watchdog thread, and is asynchronous from the
+  perspective of the main thread.
+
+  compute_duration defaults to true since retire_id is only called in the
+  watchdog thread, which is currently a place we call cuda APIs which may hang,
+  but care should be taken to avoid computing duration in any function that must
+  never hang. (timing must also be enabled for compute_duration - see
+  TORCH_NCCL_ENABLE_TIMING).
+  */
+  void retire_id(c10::optional<size_t> id, bool compute_duration = true) {
     if (!enabled_ || !id) {
       return;
     }
-    std::lock_guard<std::mutex> guard(mutex_);
-    auto& entry = entries_.at(*id % max_entries_);
-    if (entry.id_ == *id) {
-      update_state(entry);
-      entry.retired_ = true;
-      entry.start_ = entry.end_ = nullptr;
+
+    bool can_compute_duration = false;
+    EventList* startEvents = nullptr;
+    EventList* endEvents = nullptr;
+    c10::optional<float> duration = c10::nullopt;
+
+    std::unique_lock<std::mutex> guard(mutex_);
+
+    Entry* entry = &entries_.at(*id % max_entries_);
+    if (entry->id_ == *id) {
+      update_state(*entry);
+
+      if (compute_duration) {
+        can_compute_duration = entry->time_discovered_completed_.has_value() &&
+            entry->start_ && entry->end_;
+        startEvents = entry->start_;
+        endEvents = entry->end_;
+      }
     }
+
+    if (can_compute_duration) {
+      // Compute duration without without holding the lock, because
+      // cudaEventDuration() can hang, and we need to acquire the lock before we
+      // can dump(), which we never want to block.
+      guard.unlock();
+      duration = getDurationFromFirstEvent(*startEvents, *endEvents);
+      guard.lock();
+
+      // Refresh the entry pointer, see if the entry has been overwritten
+      entry = &entries_.at(*id % max_entries_);
+      if (entry->id_ != *id) {
+        LOG(INFO)
+            << "retire_id abandoned for id " << *id
+            << ", event was overwritten while waiting to compute duration.";
+        return;
+      }
+      if (duration.has_value()) {
+        entry->duration_ = duration.value();
+      }
+    }
+
+    entry->retired_ = true;
+    entry->start_ = entry->end_ = nullptr;
   }
 
-  std::string dump() {
+  std::string dump(
+      const c10::optional<std::unordered_map<
+          std::string,
+          std::unordered_map<std::string, std::string>>>& ncclDumpMap) {
     auto result = dump_entries();
     auto entries = new_list();
-    c10::IValue pg_id_s = "pg_id";
-    c10::IValue seq_id_s = "seq_id";
-    c10::IValue profiling_name_s = "profiling_name";
-    c10::IValue input_sizes_s = "input_sizes";
-    c10::IValue output_sizes_s = "output_sizes";
-    c10::IValue time_created_s = "time_created_us";
+    c10::IValue entries_key = "entries";
+    c10::IValue nccl_comm_key = "nccl_comm_state";
+    c10::IValue version_key = "version";
+    // Update whenever changing contents or formatting of the dump
+    // (minor when adding fields, major when changing existing fields)
+    c10::IValue version_val = "1.1";
 
-    c10::IValue frames_s = "frames";
-    c10::IValue state_s = "state";
-    c10::IValue line_s = "line";
-    c10::IValue name_s = "name";
-    c10::IValue filename_s = "filename";
-    c10::IValue retired_s = "retired";
+    c10::IValue pg_id_key = "pg_id";
+    c10::IValue pg_name_key = "process_group";
+    c10::IValue seq_id_key = "seq_id";
+    c10::IValue profiling_name_key = "profiling_name";
+    c10::IValue input_sizes_key = "input_sizes";
+    c10::IValue output_sizes_key = "output_sizes";
+    c10::IValue time_created_key = "time_created_ns";
+    c10::IValue duration_key = "duration_ms";
+
+    c10::IValue frames_key = "frames";
+    c10::IValue state_key = "state";
+    c10::IValue line_key = "line";
+    c10::IValue name_key = "name";
+    c10::IValue filename_key = "filename";
+    c10::IValue retired_key = "retired";
+    c10::IValue time_discovered_started_key = "time_discovered_started_ns";
+    c10::IValue time_discovered_completed_key = "time_discovered_completed_ns";
 
     std::vector<torch::CapturedTraceback*> tracebacks;
     for (auto& e : result) {
@@ -494,9 +615,9 @@ struct NCCLTraceBuffer {
     std::vector<c10::IValue> all_frames;
     for (const auto& f : stracebacks.all_frames) {
       auto d = new_dict();
-      d.insert(name_s, f.funcname);
-      d.insert(filename_s, f.filename);
-      d.insert(line_s, int64_t(f.lineno));
+      d.insert(name_key, f.funcname);
+      d.insert(filename_key, f.filename);
+      d.insert(line_key, int64_t(f.lineno));
       all_frames.emplace_back(std::move(d));
     }
 
@@ -504,10 +625,14 @@ struct NCCLTraceBuffer {
       auto& e = result.at(i);
       auto& tb = stracebacks.tracebacks.at(i);
       auto dict = new_dict();
-      dict.insert(pg_id_s, int64_t(e.pg_id_));
-      dict.insert(seq_id_s, int64_t(e.seq_id_));
-      dict.insert(profiling_name_s, e.profiling_name_);
-      dict.insert(time_created_s, int64_t(e.time_created_ / 1000));
+      dict.insert(pg_id_key, int64_t(e.pg_id_));
+      dict.insert(pg_name_key, e.pg_name_);
+      dict.insert(seq_id_key, int64_t(e.seq_id_));
+      dict.insert(profiling_name_key, e.profiling_name_);
+      dict.insert(time_created_key, int64_t(e.time_created_));
+      if (e.duration_) {
+        dict.insert(duration_key, *e.duration_);
+      }
 
       auto it = e.sizes_.begin();
       auto read_sizes = [&](const c10::SmallVector<int, 4>& dims) {
@@ -523,19 +648,55 @@ struct NCCLTraceBuffer {
         return sizes;
       };
 
-      dict.insert(input_sizes_s, read_sizes(e.input_dims_));
-      dict.insert(output_sizes_s, read_sizes(e.output_dims_));
-      dict.insert(state_s, e.state_);
-      dict.insert(retired_s, e.retired_);
+      dict.insert(input_sizes_key, read_sizes(e.input_dims_));
+      dict.insert(output_sizes_key, read_sizes(e.output_dims_));
+      if (e.time_discovered_completed_.has_value()) {
+        dict.insert(state_key, "completed");
+      } else if (e.time_discovered_started_.has_value()) {
+        dict.insert(state_key, "started");
+      } else {
+        dict.insert(state_key, "scheduled");
+      }
+
+      dict.insert(
+          time_discovered_started_key,
+          e.time_discovered_started_.has_value()
+              ? int64_t(*e.time_discovered_started_)
+              : c10::IValue());
+      dict.insert(
+          time_discovered_completed_key,
+          e.time_discovered_completed_.has_value()
+              ? int64_t(*e.time_discovered_completed_)
+              : c10::IValue());
+      dict.insert(retired_key, e.retired_);
 
       auto frames = new_list();
       for (int64_t frame : tb) {
         frames.push_back(all_frames.at(frame));
       }
-      dict.insert(frames_s, frames);
+      dict.insert(frames_key, frames);
       entries.push_back(dict);
     }
-    return pickle_str(entries);
+    // convert ncclDumpMap into a dictionary
+    auto per_comm_dict = new_dict();
+    if (ncclDumpMap.has_value()) {
+      for (const auto& [ncclId, ncclDump] : ncclDumpMap.value()) {
+        auto inner_dict = new_dict();
+        for (const auto& [key, value] : ncclDump) {
+          inner_dict.insert(key, value);
+        }
+        per_comm_dict.insert(ncclId, inner_dict);
+      }
+    }
+
+    auto dict = new_dict();
+    dict.insert(entries_key, entries);
+    dict.insert(version_key, version_val);
+    if (per_comm_dict.size() > 0) {
+      dict.insert(nccl_comm_key, per_comm_dict);
+    }
+
+    return pickle_str(dict);
   }
 };
 

torch/csrc/distributed/c10d/init.cpp

@@ -50,6 +50,35 @@
 
 namespace {
 
+#ifdef USE_C10D_NCCL
+
+bool acquire_gil() {
+  // basically if this function can acquire the gil, it will return quickly.
+  // if not, it will hang forever.  The idea is to call this from a thread
+  // wrapped in a future, and then check the future after a timeout, to
+  // determine whether we're facing gil contention.
+  if (Py_IsInitialized()) {
+    pybind11::gil_scoped_acquire gil;
+    return true;
+  }
+
+  // If we end up here, its probably still a "pass" from the perspective of
+  // checking whether python is stuck. but currently we don't check the return
+  // value of this function anyway, just check whether it returned quickly vs
+  // timing out.  Taking a long time is the main sign of trouble.  Fast return
+  // with true or with false is both OK from the perspective of debugging python
+  // hangs.
+  return false;
+}
+
+bool registerGilChecker() {
+  c10d::get_gil_checker() = &acquire_gil;
+  return true;
+}
+
+static bool registered = registerGilChecker();
+#endif // USE_C10D_NCCL
+
 // Wrapper to ensure GIL is released before destructing ProcessGroupGloo
 // TODO: move this somewhere more generally useful
 template <typename T>
@@ -1033,6 +1062,29 @@ Example::
     >>> store.add("first_key", 6)
     >>> # Should return 7
     >>> store.get("first_key")
+)")
+          .def(
+              "check",
+              &::c10d::Store::check,
+              py::call_guard<py::gil_scoped_release>(),
+              R"(
+The call to check whether a given list of ``keys`` have value stored in
+the store. This call immediately returns in normal cases but still suffers
+from some edge deadlock cases, e.g, calling check after TCPStore has been destroyed.
+Calling :meth:`~torch.distributed.store.check` with a list of keys that
+one wants to check whether stored in the store or not.
+
+Arguments:
+    keys (lisr[str]): The keys to query whether stored in the store.
+
+Example::
+    >>> import torch.distributed as dist
+    >>> from datetime import timedelta
+    >>> # Using TCPStore as an example, other store types can also be used
+    >>> store = dist.TCPStore("127.0.0.1", 0, 1, True, timedelta(seconds=30))
+    >>> store.add("first_key", 1)
+    >>> # Should return 7
+    >>> store.check(["first_key"])
 )")
           .def(
               "delete_key",
@@ -1404,7 +1456,11 @@ Arguments:
       .def_property_readonly(
           "underlying_store",
           &::c10d::PrefixStore::getUnderlyingStore,
-          R"(Gets the underlying store object that PrefixStore wraps around.)");
+          R"(Gets the underlying store object that PrefixStore wraps around.)")
+      .def_property_readonly(
+          "_underlying_non_prefix_store",
+          &::c10d::PrefixStore::getUnderlyingNonPrefixStore,
+          R"(Recursively to get the store before layers of wrapping with PrefixStore.)");
 
   auto processGroup =
       py::class_<
@@ -1807,6 +1863,15 @@ Arguments:
               "group_name",
               &::c10d::ProcessGroup::getGroupName,
               "(Gets this process group name. It's cluster unique)")
+          .def(
+              "_set_group_desc",
+              &::c10d::ProcessGroup::setGroupDesc,
+              py::call_guard<py::gil_scoped_acquire>(),
+              "Sets the process group description. This is an internal C10D method, do not use.")
+          .def_property_readonly(
+              "group_desc",
+              &::c10d::ProcessGroup::getGroupDesc,
+              "Gets this process group description")
           .def_property(
               "bound_device_id",
               &::c10d::ProcessGroup::getBoundDeviceId,
@@ -2387,7 +2452,9 @@ Example::
       .def_readwrite(
           "split_from", &::c10d::ProcessGroupNCCL::Options::split_from)
       .def_readwrite(
-          "split_color", &::c10d::ProcessGroupNCCL::Options::split_color);
+          "split_color", &::c10d::ProcessGroupNCCL::Options::split_color)
+      .def_readwrite(
+          "group_name", &::c10d::ProcessGroupNCCL::Options::group_name);
 
 #endif
 

torch/distributed/_state_dict_utils.py

@@ -0,0 +1,448 @@
+import io
+import math
+from typing import Any, Callable, Dict, Optional, Tuple, TYPE_CHECKING
+
+import torch
+import torch.distributed as dist
+import torch.nn.functional as F
+from torch.distributed._functional_collectives import AsyncCollectiveTensor
+
+if dist.is_available() or TYPE_CHECKING:
+    from torch.distributed import distributed_c10d
+    from torch.distributed._shard.sharded_tensor import ShardedTensor
+    from torch.distributed._tensor import DTensor, Replicate
+
+
+def _identity_func(
+    obj: torch.Tensor,
+    pg: Optional[dist.ProcessGroup],
+    device: Optional[torch.device],
+    companion_obj: Any,
+) -> torch.Tensor:
+    return obj
+
+
+def _all_gather_sharded_tensor(
+    sharded_tensor: "ShardedTensor",
+    pg: Optional[dist.ProcessGroup] = None,
+    device: Optional[torch.device] = None,
+) -> torch.Tensor:
+    if pg is None:
+        pg = distributed_c10d._get_default_group()
+    world_size = dist.get_world_size(pg)
+    shards = sharded_tensor.local_shards()
+    dim_0_size = sharded_tensor.size()[0]  # type: ignore[index]
+    tensor_numel = sharded_tensor.size().numel()  # type: ignore[union-attr]
+    chunk_size = math.ceil(dim_0_size / world_size) * tensor_numel // dim_0_size
+    pg_device = (
+        distributed_c10d._get_pg_default_device(pg) if device is None else device
+    )
+    if shards:
+        local_tensor = shards[0].tensor.flatten()
+        if local_tensor.device.type != pg_device.type:
+            local_tensor = local_tensor.to(pg_device)
+        num_padding = chunk_size - local_tensor.numel()
+        if num_padding > 0:
+            local_tensor = F.pad(local_tensor, [0, num_padding])
+    else:
+        local_tensor = torch.zeros(
+            chunk_size, dtype=sharded_tensor.dtype, device=pg_device
+        )
+
+    tensor = torch.empty(
+        chunk_size * world_size,
+        dtype=local_tensor.dtype,
+        device=pg_device,
+    )
+    dist.all_gather_into_tensor(tensor, local_tensor, group=pg)
+
+    tensor = tensor.narrow(0, 0, tensor_numel).reshape(sharded_tensor.size())
+    return tensor
+
+
+class CompanionMismatch(Exception):
+    ...
+
+
+def _iterate_state_dict(
+    iter_object: Any,
+    sharded_tensor_func: Callable,
+    dtensor_func: Callable,
+    tensor_func: Callable,
+    *,
+    pg: Optional[dist.ProcessGroup] = None,
+    device: Optional[torch.device] = None,
+    cpu_offload: bool = False,
+    companion_obj: Any = None,
+    ranks_only: Tuple[int, ...] = tuple(),
+    type_check: bool = True,
+    non_blocking: bool = True,
+) -> Dict[str, Any]:
+    """Iterate through the state dict, applying the given functions to each tensor type.
+
+    Args:
+        iter_object (Any): the target state_dict.
+        sharded_tensor_func (Callable): the function to apply to ShardedTensor
+        dtensor_func (Callable): the function to apply to DTensor
+        tensor_func (Callable): the function to apply to Tensor
+        pg (Optional[dist.ProcessGroup]): process group passed to tensor functions
+        device (Optional[torch.device]): device passed to tensor functions
+        cpu_offload (bool): whether to offload the tensors to CPU memory. This option is ignored
+            if a companion_obj is supplied.
+        companion_obj (Any): A companion object to the state dict. If this object
+            is supplied, we attempt to copy the tensor to the companion object.
+        ranks_only (Tuple[int, ...]): if this tuple is empty, all ranks will
+            have the same state_dicts. Otherwise only ranks that in ``ranks_only``
+            have the same state_dicts. Other ranks will get empty state_dicts.
+        type_check (bool): check if the instance data type is a supported type
+            that can be saved by DCP.  The current supported data types are
+            torch.Tensor, DTensor, int, float, str, list, dict, None.
+        non_blocking (bool): whether to use non-blocking copy when copying to the companion object.
+    """
+    # TODO: should we use pytree?
+    cpu_device = torch.device("cpu")
+    if isinstance(iter_object, ShardedTensor):
+        ret = sharded_tensor_func(iter_object, pg, device, companion_obj)
+    elif isinstance(iter_object, DTensor):
+        ret = dtensor_func(iter_object, pg, device, companion_obj)
+    elif isinstance(iter_object, torch.Tensor):
+        ret = tensor_func(iter_object, pg, device, companion_obj)
+    elif (
+        isinstance(iter_object, (int, float, str, bytes, io.BytesIO))
+        or iter_object is None
+    ):
+        ret = iter_object
+    elif isinstance(iter_object, dict):
+        if companion_obj is not None and (
+            not isinstance(companion_obj, dict)
+            or set(companion_obj.keys()) != set(iter_object.keys())
+        ):
+            raise CompanionMismatch()
+
+        ret = {
+            key: _iterate_state_dict(
+                value,
+                sharded_tensor_func,
+                dtensor_func,
+                tensor_func,
+                pg=pg,
+                device=device,
+                cpu_offload=cpu_offload,
+                companion_obj=companion_obj[key] if companion_obj is not None else None,
+                ranks_only=ranks_only,
+                type_check=type_check,
+                non_blocking=non_blocking,
+            )
+            for key, value in iter_object.items()
+        }
+    elif isinstance(iter_object, (list, tuple)):
+        if companion_obj is not None and (
+            not isinstance(companion_obj, (list, tuple))
+            or len(companion_obj) != len(iter_object)
+        ):
+            raise CompanionMismatch()
+
+        ret = [
+            _iterate_state_dict(
+                v,
+                sharded_tensor_func,
+                dtensor_func,
+                tensor_func,
+                pg=pg,
+                device=device,
+                cpu_offload=cpu_offload,
+                companion_obj=companion_obj[idx] if companion_obj is not None else None,
+                ranks_only=ranks_only,
+                type_check=type_check,
+                non_blocking=non_blocking,
+            )
+            for idx, v in enumerate(iter_object)
+        ]
+        if isinstance(iter_object, tuple):
+            ret = tuple(ret)
+    elif not type_check:
+        ret = iter_object
+    else:
+        raise ValueError(f"Unexpected value type {type(iter_object)}")
+
+    if not ranks_only or dist.get_rank(pg) in ranks_only:
+        if isinstance(ret, torch.Tensor):
+            if cpu_offload and companion_obj is None:
+                ret = ret.to(cpu_device)
+
+            if companion_obj is not None:
+                # TODO: support DTensor
+                companion_obj.copy_(ret, non_blocking=non_blocking)
+                ret = companion_obj
+    else:
+        ret = {} if isinstance(ret, dict) else None
+
+    return ret
+
+
+def _gather_state_dict(
+    state_dict: Dict[str, Any],
+    *,
+    pg: Optional[dist.ProcessGroup] = None,
+    device: Optional[torch.device] = None,
+    cpu_offload: bool = False,
+    ranks_only: Tuple[int, ...] = tuple(),
+    type_check: bool = True,
+) -> Dict[str, Any]:
+    """
+    Given a state_dict, this API gathers all the ShardedTensors or DTensors in
+    the state_dict.
+
+
+    Args:
+        state_dict (Dict[str, Any]): the target sharded state_dict.
+        pg (Optional[dist.ProcessGroup]): the process group that is used to
+            gather ShardedTensor. Note that gathering a DTensor will use
+            the DeviceMesh. So this argument will be ignored when gathering a
+            DTensor.
+        device: (Optional[torch.device]): the device that is used to
+            perform allgather for ShardedTensor. Note that gathering a DTensor
+            will use the DeviceMesh. So this argument will be ignored when
+            gathering a DTensor.
+        cpu_offload (bool): whether to offload the tensors to CPU memory. The
+            default value is False.
+        ranks_only: (Tuple[int, ...]): if this tuple is empty, all ranks will
+            have the same state_dicts. Otherwise only ranks that in ``ranks_only``
+            have the same state_dicts. Other ranks will get empty state_dicts.
+        type_check: (bool): check if the instance data type is a supported type
+            that can be saved by DCP.  The current supported data types are
+            torch.Tensor, DTensor, int, float, str, list, dict, None.
+
+    Returns:
+        The gathered state dictionary.
+    """
+
+    def sharded_tensor_func(value, pg, device, companion_obj):
+        # ShardedTensor does not seem to record the original device type.
+        # So if the tensor is moved to CPU, we won't know the original type.
+        # As a result, we have to rely on the user to tell us the correct one.
+        cpu_device = torch.device("cpu")
+        output_tensor = _all_gather_sharded_tensor(value, pg, device)
+        local_shard_device = (
+            value.local_shards()[0].tensor.device
+            if value.local_shards()
+            else cpu_device
+        )
+        if output_tensor.device != local_shard_device:
+            value = output_tensor.to(local_shard_device)
+        else:
+            value = output_tensor
+        return value
+
+    def dtensor_func(value, pg, device, companion_obj):
+        if value.device != value.device_mesh.device_type:
+            value = value.to(value.device_mesh.device_type)
+        # FSDP all_gather: [Shard(0)] -> [Replicate()]
+        # HSDP all_gather: [Replicate(), Shard(0)] -> [Replicate(), Replicate()]
+        # 2D FSDP + TP all_gather:
+        # - [Shard(0), Shard(n)] -> [Replicate(), Replicate()]
+        # - [Shard(0), Replicate()] -> [Replicate(), Replicate()]
+        placements = [Replicate() for _ in value.placements]
+        value = value.redistribute(
+            device_mesh=value.device_mesh,
+            placements=placements,
+        )
+        # Call `wait()` to force the tensor to be synchronous with respect
+        # to the main stream.
+        # See the discussion in https://github.com/pytorch/pytorch/pull/117799.
+        value = value.to_local()
+        if isinstance(value, AsyncCollectiveTensor):
+            value = value.wait()
+        return value
+
+    return _iterate_state_dict(
+        state_dict,
+        sharded_tensor_func,
+        dtensor_func,
+        _identity_func,
+        pg=pg,
+        device=device,
+        cpu_offload=cpu_offload,
+        ranks_only=ranks_only,
+        type_check=type_check,
+    )
+
+
+def _offload_state_dict_to_cpu(
+    state_dict: Dict[str, Any],
+    *,
+    ranks_only: Tuple[int, ...] = tuple(),
+    type_check: bool = True,
+) -> Dict[str, Any]:
+    """
+    Given a state_dict, this API offload all the tensors to CPU memory.
+
+    Args:
+        state_dict (Dict[str, Any]): the target state_dict.
+        pg (Optional[dist.ProcessGroup]): the process group that is used to
+            gather ShardedTensor. Note that gathering a DTensor will use
+            the DeviceMesh. So this argument will be ignored when gathering a
+            DTensor.
+        ranks_only: (Tuple[int, ...]): if this tuple is empty, all ranks will
+            have the same state_dicts. Otherwise only ranks that in ``ranks_only``
+            have the same state_dicts. Other ranks will get empty state_dicts.
+        type_check: (bool): check if the instance data type is a supported type
+            that can be saved by DCP.  The current supported data types are
+            torch.Tensor, DTensor, int, float, str, list, dict, None.
+
+    Returns:
+        The gathered state dictionary.
+    """
+
+    ret = _iterate_state_dict(
+        state_dict,
+        _identity_func,
+        _identity_func,
+        _identity_func,
+        pg=None,
+        device=None,
+        cpu_offload=True,
+        ranks_only=ranks_only,
+        type_check=type_check,
+    )
+    return ret
+
+
+def _copy_state_dict(
+    state_dict: Dict[str, Any],
+    copy_state_dict: Dict[str, Any],
+    non_blocking: bool = False,
+):
+    """
+    Copies all tensors in a given state dict into a different state_dict with the
+    same structure.
+
+    .. warning::
+        It is expected by this function that state_dict and copy_state_dict share
+        the same structure and data types.
+
+    .. warning::
+        The current supported data types are
+            torch.Tensor, DTensor, int, float, str, list, dict, None.
+
+    Args:
+        state_dict (Dict[str, Any]): the target state_dict.
+        copy_state_dict (Dict[str, Any]):
+            The state dict we are copying into. This state_dict must have exactly
+             the same structure as the source `state_dict`.
+        non_blocking: (bool): Whether copy ops should be performed asynchronously
+    """
+
+    _iterate_state_dict(
+        state_dict,
+        _identity_func,
+        _identity_func,
+        _identity_func,
+        pg=None,
+        device=None,
+        cpu_offload=False,
+        ranks_only=tuple(),
+        companion_obj=copy_state_dict,
+        type_check=True,
+        non_blocking=non_blocking,
+    )
+
+
+def _create_cpu_state_dict(
+    state_dict: Dict[str, Any], pin_memory: bool = False, share_memory: bool = False
+) -> Dict[str, Any]:
+    """
+    Given a state_dict, create another state_dict with the same structure and elements.
+    However, all tensors in the returned state_dict are new tensors on CPU. These
+    tensors can be placed on pin_memory or share_memory based on the provided arguments.
+
+    .. warning::
+        Setting both `pin_memory` and `share_memory` to True significantly increases the
+        latency of this method because of the nuances which require us to register memory
+        as pinned directly as opposed to relying on the pin_memory cache allocator. This
+        option should only be used for long lived tensors which are required to be shared.
+        This is not the case as long as at least one of `pin_memory` or `share_memory` is
+         set to False.
+
+    """
+
+    def tensor_func(
+        obj: torch.Tensor,
+        pg: Optional[dist.ProcessGroup],
+        device: Optional[torch.device],
+        _: Any,
+    ) -> torch.Tensor:
+        if len(obj.size()) == 0:
+            return torch.tensor(0, dtype=obj.dtype)
+
+        if share_memory:
+            t = torch.empty(*tuple(obj.size()), dtype=obj.dtype).share_memory_()
+            if pin_memory:
+                succ = torch.cuda.cudart().cudaHostRegister(
+                    t.data_ptr(),
+                    t.numel() * t.element_size(),
+                    1,  # lines up with 'cudaHostRegisterPortable'
+                )
+                assert (
+                    succ == 0
+                ), f"Pinning shared memory failed with error-code: {succ}"
+            return t
+        elif pin_memory:
+            return torch.empty(*tuple(obj.size()), dtype=obj.dtype).pin_memory()
+        else:
+            return torch.empty(*tuple(obj.size()), dtype=obj.dtype)
+
+    ret = _iterate_state_dict(
+        state_dict,
+        _identity_func,
+        _identity_func,
+        tensor_func,
+        pg=None,
+        device=None,
+        cpu_offload=False,
+        ranks_only=tuple(),
+        type_check=False,
+    )
+    return ret
+
+
+def _check_state_dict_similarity(
+    state_dict: Dict[str, Any],
+    compared_state_dict: Dict[str, Any],
+) -> bool:
+    """
+    Given two state_dicts, check if the structures are the same. And
+    if a [key, tensor] pair exist in one state_dict there must be
+    the a corresponding pait, [key, other_tensor], in the other state_dict,
+    where tensor and other_tensor have the same size and dtype.
+
+    Return the check result.
+    """
+
+    def tensor_func(
+        obj: torch.Tensor,
+        pg: Optional[dist.ProcessGroup],
+        device: Optional[torch.device],
+        companion_obj: Any,
+    ) -> torch.Tensor:
+        if companion_obj.dtype != obj.dtype or companion_obj.size() != obj.size():
+            raise CompanionMismatch()
+        return obj
+
+    try:
+        _iterate_state_dict(
+            state_dict,
+            _identity_func,
+            _identity_func,
+            tensor_func,
+            pg=None,
+            device=None,
+            cpu_offload=False,
+            ranks_only=tuple(),
+            companion_obj=compared_state_dict,
+            type_check=False,
+        )
+    except CompanionMismatch:
+        return False
+
+    return True

torch/distributed/distributed_c10d.py

@@ -1171,7 +1171,7 @@ def init_process_group(
             )
 
         default_pg, _ = _new_process_group_helper(
-            -1, -1, [], backend, None, group_name, timeout=timeout
+            -1, -1, [], backend, None, group_name, timeout=timeout, group_desc="default_pg"
         )
         _update_default_pg(default_pg)
     else:
@@ -1197,6 +1197,7 @@ def init_process_group(
             pg_options=pg_options,
             timeout=timeout,
             device_id=device_id,
+            group_desc="default_pg"
         )
         _update_default_pg(default_pg)
 
@@ -1257,6 +1258,7 @@ def _new_process_group_helper(
     timeout=None,
     pg_tag=None,
     device_id=None,
+    group_desc=None,
 ):
     """
     Create a new distributed process group.
@@ -1289,6 +1291,8 @@ def _new_process_group_helper(
             _, prefix_store = _world.pg_map[existing_group]
             return existing_group, prefix_store
 
+    group_desc = "undefined" if group_desc is None else group_desc
+
     # The list of group ranks is empty if we're creating the default group.
     is_default_group = len(global_ranks_in_group) == 0
 
@@ -1375,6 +1379,7 @@ def _new_process_group_helper(
             if split_from:
                 pg_options.split_from = split_from
                 pg_options.split_color = _process_group_color(global_ranks_in_group)
+            pg_options.group_name = group_name
             backend_class = ProcessGroupNCCL(
                 backend_prefix_store, group_rank, group_size, pg_options)
             backend_type = ProcessGroup.BackendType.NCCL
@@ -1461,9 +1466,11 @@ def _new_process_group_helper(
 
     # update global state
     assert group_name is not None
+    assert group_desc is not None
     _world.pg_map[pg] = (backend, prefix_store)
     _world.pg_names[pg] = group_name
     pg._set_group_name(group_name)
+    pg._set_group_desc(group_desc)
 
     _world.pg_backend_config[pg] = str(backend_config)
     # "" is the default tag for user PGs
@@ -3614,7 +3621,7 @@ def _get_backend_from_str(backend: Optional[str] = None) -> Backend:
 
 
 @_time_logger
-def new_group(ranks=None, timeout=None, backend=None, pg_options=None, use_local_synchronization=False):
+def new_group(ranks=None, timeout=None, backend=None, pg_options=None, use_local_synchronization=False, group_desc=None):
     """
     Create a new distributed group.
 
@@ -3655,6 +3662,7 @@ def new_group(ranks=None, timeout=None, backend=None, pg_options=None, use_local
             barrier at the end of the process group creation. This is different
             in that non-member ranks don't need to call into API and don't
             join the barrier.
+        group_desc (str, optional): a string to describe the process group.
 
     Returns:
         A handle of distributed group that can be given to collective calls or None if the rank is not part of ``ranks``.
@@ -3669,7 +3677,15 @@ def new_group(ranks=None, timeout=None, backend=None, pg_options=None, use_local
     multiple overlaping process groups. To avoid that, make sure all ranks follow the
     same global creation order.
     """
-    return _new_group_with_tag(ranks, timeout, backend, pg_options, None, use_local_synchronization=use_local_synchronization)
+    return _new_group_with_tag(
+        ranks,
+        timeout,
+        backend,
+        pg_options,
+        None,
+        use_local_synchronization=use_local_synchronization,
+        group_desc=group_desc,
+    )
 
 def _new_group_with_tag(
     ranks=None,
@@ -3677,7 +3693,8 @@ def _new_group_with_tag(
     backend=None,
     pg_options=None,
     pg_tag=None,
-    use_local_synchronization=False
+    use_local_synchronization=False,
+    group_desc=None
 ):
     """
     Variant of ``new_group`` that exposes tag creation.
@@ -3749,7 +3766,8 @@ def _new_group_with_tag(
         group_name,
         pg_options=pg_options,
         timeout=timeout,
-        pg_tag=pg_tag
+        pg_tag=pg_tag,
+        group_desc=group_desc
     )
 
     # Create the global rank to group rank mapping
@@ -3789,6 +3807,7 @@ def new_subgroups(
     timeout=None,
     backend=None,
     pg_options=None,
+    group_desc=None,
 ):
     """
     Create subgroups of equal size.
@@ -3841,6 +3860,8 @@ def new_subgroups(
             the construction of specific process groups. i.e. for the ``nccl``
             backend, ``is_high_priority_stream`` can be specified so that
             process group can pick up high priority cuda streams.
+        group_desc (str, optional): A string describing the group. Each subgroup will
+            inherit its group_desc
 
     Returns:
         The subgroup containing the current rank, and all the subgroups used for cleanup.
@@ -3886,6 +3907,7 @@ def new_subgroups(
             timeout=timeout,
             backend=backend,
             pg_options=pg_options,
+            group_desc=group_desc,
         )
         subgroups.append(subgroup)
 
@@ -3905,6 +3927,7 @@ def new_subgroups_by_enumeration(
     timeout=None,
     backend=None,
     pg_options=None,
+    group_desc=None,
 ):
     """
     Create subgroups by dividing the global world.
@@ -3945,6 +3968,8 @@ def new_subgroups_by_enumeration(
             the construction of specific process groups. i.e. for the ``nccl``
             backend, ``is_high_priority_stream`` can be specified so that
             process group can pick up high priority cuda streams.
+        group_desc (str, optional): A string describing the group. Each subgroup will
+            inherit its group_desc.
 
     Returns:
         The subgroup containing the current rank, and all the subgroups used for cleanup.
@@ -3973,6 +3998,7 @@ def new_subgroups_by_enumeration(
             timeout=timeout,
             backend=backend,
             pg_options=pg_options,
+            group_desc=group_desc,
         )
         subgroups.append(subgroup)
         my_rank = get_rank()

torch/distributed/elastic/multiprocessing/tail_log.py

@@ -28,7 +28,7 @@ def tail_logfile(
             return
         time.sleep(interval_sec)
 
-    with open(file) as fp:
+    with open(file, errors="replace") as fp:
         while True:
             line = fp.readline()