distributed/debug: add an HTTP server for debugging running jobs

.ci/docker/requirements-ci.txt

@@ -402,3 +402,6 @@ scikit-build==0.18.1
 pyre-extensions==0.0.32
 tabulate==0.9.0
 #Description: These package are needed to build FBGEMM and torchrec on PyTorch CI
+
+Flask==3.1.2
+#Description: required for torch.distributed.debug

test/distributed/test_debug.py

@@ -0,0 +1,50 @@
+# Owner(s): ["oncall: distributed"]
+
+import os
+
+import requests
+from requests.adapters import HTTPAdapter
+from urllib3.util.retry import Retry
+
+import torch.distributed as dist
+from torch.distributed.debug import start_debug_server, stop_debug_server
+from torch.testing._internal.common_utils import run_tests, TestCase
+
+
+session = requests.Session()
+retry_strategy = Retry(total=5, backoff_factor=0.5)
+adapter = HTTPAdapter(max_retries=retry_strategy)
+session.mount("http://", adapter)
+session.mount("https://", adapter)
+
+
+class TestDebug(TestCase):
+    def test_basics(self) -> None:
+        store = dist.TCPStore("localhost", 0, 1, is_master=True, wait_for_workers=False)
+        os.environ["MASTER_ADDR"] = "localhost"
+        os.environ["MASTER_PORT"] = str(store.port)
+        os.environ["RANK"] = "0"
+        os.environ["WORLD_SIZE"] = "1"
+
+        port = 25999
+
+        def fetch(path: str) -> str:
+            resp = session.get(f"http://localhost:{port}{path}")
+            resp.raise_for_status()
+            return resp.text
+
+        print("starting!")
+
+        start_debug_server(port=port)
+
+        self.assertIn("torch profiler", fetch("/"))
+        self.assertIn("View 0", fetch("/profile?duration=0.01"))
+        self.assertIn("test_basics", fetch("/stacks"))
+        self.assertIn("pg_status", fetch("/fr_trace"))
+        self.assertIn("pg_status", fetch("/fr_trace_nccl"))
+
+        stop_debug_server()
+
+
+if __name__ == "__main__":
+    run_tests()

torch/_C/_distributed_c10d.pyi

@@ -100,7 +100,9 @@ class Logger:
     def _set_static_graph(self) -> None: ...
 
 class _WorkerServer:
-    def __init__(self, socket_path: str) -> None: ...
+    port: int
+
+    def __init__(self, host_or_file: str, port: int = ...) -> None: ...
     def shutdown(self) -> None: ...
 
 def get_debug_level(): ...
@@ -206,6 +208,7 @@ class Store:
         desired_value: str,
     ) -> bytes: ...
     def delete_key(self, key: str) -> bool: ...
+    def multi_get(self, keys: list[str]) -> list[bytes]: ...
     def num_keys(self) -> int: ...
     def set_timeout(self, timeout: timedelta): ...
     @overload
@@ -871,3 +874,15 @@ class ProcessGroupXCCL(Backend):
 
 def _set_process_group(pg: ProcessGroup) -> None: ...
 def _current_process_group() -> ProcessGroup: ...
+
+class _Request:
+    def body(self) -> bytes: ...
+    def get_param(self, str) -> str: ...
+
+class _Response:
+    def set_content(self, content: str | bytes, content_type: str) -> None: ...
+    def set_status(self, status: int) -> None: ...
+
+def _register_handler(
+    name: str, handler: Callable[[_Request, _Response], None]
+) -> None: ...

torch/_C/_profiler.pyi

@@ -60,6 +60,7 @@ class _ExperimentalConfig:
         verbose: bool = ...,
         performance_events: list[str] = ...,
         enable_cuda_sync_events: bool = ...,
+        profile_all_threads: bool = ...,
     ) -> None: ...
 
 class ProfilerConfig:

torch/csrc/distributed/c10d/control_plane/Handlers.cpp

@@ -1,5 +1,7 @@
 #include <torch/csrc/distributed/c10d/control_plane/Handlers.hpp>
 
+#include <torch/csrc/distributed/c10d/FlightRecorder.hpp>
+
 #include <fmt/format.h>
 #include <mutex>
 #include <shared_mutex>
@@ -63,6 +65,14 @@ RegisterHandler pingHandler{"ping", [](const Request&, Response& res) {
                               res.setStatus(200);
                             }};
 
+RegisterHandler frTracehandler(
+    "fr_trace_json",
+    [](const Request&, Response& res) {
+      auto trace = ::c10d::dump_fr_trace_json(true, true);
+      res.setContent(std::move(trace), "application/json");
+      res.setStatus(200);
+    });
+
 } // namespace
 
 void registerHandler(const std::string& name, HandlerFunc f) {

torch/csrc/distributed/c10d/control_plane/Handlers.hpp

@@ -18,6 +18,14 @@ class TORCH_API Request {
   virtual const std::string& body() const = 0;
 
   virtual const std::multimap<std::string, std::string>& params() const = 0;
+
+  std::string getParam(const std::string& key) const {
+    auto it = params().find(key);
+    if (it != params().end()) {
+      return it->second;
+    }
+    return "";
+  }
 };
 
 // Response represents a response to the handler. This conceptually maps to an

torch/csrc/distributed/c10d/control_plane/WorkerServer.cpp

@@ -152,11 +152,17 @@ WorkerServer::WorkerServer(const std::string& hostOrFile, int port) {
     TORCH_CHECK(
         server_.bind_to_port(hostOrFile, 80),
         fmt::format("Error binding to {}", hostOrFile));
+  } else if (port == 0) {
+    C10D_WARNING("Server listening to TCP {}:{}", hostOrFile, port);
+    port_ = server_.bind_to_any_port(hostOrFile);
+    TORCH_CHECK(
+        port_ >= 0, fmt::format("Error binding to {}:{}", hostOrFile, port));
   } else {
     C10D_WARNING("Server listening to TCP {}:{}", hostOrFile, port);
     TORCH_CHECK(
         server_.bind_to_port(hostOrFile, port),
         fmt::format("Error binding to {}:{}", hostOrFile, port));
+    port_ = port;
   }
 
   serverThread_ = std::thread([this]() {

torch/csrc/distributed/c10d/control_plane/WorkerServer.hpp

@@ -19,9 +19,14 @@ class TORCH_API WorkerServer : public c10::intrusive_ptr_target {
 
   void shutdown();
 
+  int port() {
+    return port_;
+  }
+
  private:
   httplib::Server server_;
   std::thread serverThread_;
+  int port_;
 };
 
 } // namespace c10d::control_plane

torch/csrc/distributed/c10d/init.cpp

@@ -46,6 +46,7 @@
 
 #include <fmt/format.h>
 #include <pybind11/chrono.h>
+#include <pybind11/functional.h>
 #include <torch/csrc/distributed/c10d/PrefixStore.hpp>
 #include <torch/csrc/distributed/c10d/symm_mem/DMAConnectivity.hpp>
 #include <torch/csrc/distributed/c10d/symm_mem/SymmetricMemory.hpp>
@@ -4203,7 +4204,9 @@ such as `dist.all_reduce(tensor, async_op=True)`.
           }),
           py::arg("host_or_file"),
           py::arg("port") = -1)
-      .def("shutdown", &::c10d::control_plane::WorkerServer::shutdown);
+      .def("shutdown", &::c10d::control_plane::WorkerServer::shutdown)
+      .def_property_readonly(
+          "port", &::c10d::control_plane::WorkerServer::port);
 
   module.def(
       "_get_handler",
@@ -4219,6 +4222,25 @@ such as `dist.all_reduce(tensor, async_op=True)`.
       Returns the handler with the specified name.
     )");
 
+  module.def(
+      "_register_handler",
+      [](const std::string& name, const py::function& handler) {
+        ::c10d::control_plane::registerHandler(
+            name,
+            [handler](
+                const ::c10d::control_plane::Request& req,
+                ::c10d::control_plane::Response& res) {
+              py::gil_scoped_acquire acquire;
+              handler(std::ref(req), std::ref(res));
+            });
+      },
+
+      py::arg("name"),
+      py::arg("handler"),
+      R"(
+    Registers a handler by name.
+  )");
+
   module.def(
       "_get_handler_names",
       &::c10d::control_plane::getHandlerNames,
@@ -4236,12 +4258,9 @@ such as `dist.all_reduce(tensor, async_op=True)`.
       // Default constructor.
       .def(py::init<>())
       .def("body", &::c10d::control_plane::Request::body)
-      .def("params", &::c10d::control_plane::Request::params);
+      .def("get_param", &::c10d::control_plane::Request::getParam);
 
-  py::class_<
-      ::c10d::control_plane::Response,
-      std::shared_ptr<::c10d::control_plane::Response>,
-      PythonResponse>(
+  py::class_<::c10d::control_plane::Response, PythonResponse>(
       module,
       "_Response",
       R"(

torch/distributed/debug/__init__.py

@@ -0,0 +1,52 @@
+import multiprocessing
+import socket
+
+# import for registration side effect
+import torch.distributed.debug._handlers  # noqa: F401
+from torch._C._distributed_c10d import _WorkerServer
+from torch.distributed.debug._store import get_rank, tcpstore_client
+
+
+__all__ = [
+    "start_debug_server",
+    "stop_debug_server",
+]
+
+_WORKER_SERVER: _WorkerServer | None = None
+_DEBUG_SERVER_PROC: multiprocessing.Process | None = None
+
+
+def start_debug_server(port: int = 25999, worker_port: int = 0) -> None:
+    global _WORKER_SERVER, _DEBUG_SERVER_PROC
+
+    assert _WORKER_SERVER is None, "debug server already started"
+    assert _DEBUG_SERVER_PROC is None, "debug server already started"
+
+    store = tcpstore_client()
+
+    _WORKER_SERVER = _WorkerServer("::", worker_port)
+
+    RANK = get_rank()
+    store.set(f"rank{RANK}", f"http://{socket.gethostname()}:{_WORKER_SERVER.port}")
+
+    from torch.distributed.debug._flask import main
+
+    if RANK == 0:
+        _DEBUG_SERVER_PROC = multiprocessing.Process(
+            target=main, args=(port,), daemon=True
+        )
+        _DEBUG_SERVER_PROC.start()
+
+
+def stop_debug_server() -> None:
+    global _WORKER_SERVER, _DEBUG_SERVER_PROC
+
+    assert _DEBUG_SERVER_PROC is not None
+    assert _WORKER_SERVER is not None
+
+    _DEBUG_SERVER_PROC.terminate()
+    _WORKER_SERVER.shutdown()
+    _DEBUG_SERVER_PROC.join()
+
+    _WORKER_SERVER = None
+    _DEBUG_SERVER_PROC = None

torch/distributed/debug/_flask.py

@@ -0,0 +1,265 @@
+import json
+from concurrent.futures import ThreadPoolExecutor
+from typing import Iterator
+
+import requests
+from flask import Flask, render_template, request
+from jinja2 import DictLoader
+
+from torch.distributed.debug._store import get_world_size, tcpstore_client
+
+
+def fetch_all(
+    endpoint: str, args: str = ""
+) -> tuple[list[str], Iterator[requests.Response]]:
+    store = tcpstore_client()
+    keys = [f"rank{r}" for r in range(get_world_size())]
+    addrs = store.multi_get(keys)
+    addrs = [f"{addr.decode()}/handler/{endpoint}?{args}" for addr in addrs]
+
+    with ThreadPoolExecutor(max_workers=10) as executor:
+        resps = executor.map(requests.post, addrs)
+
+    return addrs, resps
+
+
+def format_json(blob: str):
+    parsed = json.loads(blob)
+    return json.dumps(parsed, indent=2)
+
+
+templates = {
+    "base.html": """
+<!doctype html>
+<head>
+    <title>{% block title %}{% endblock %} - PyTorch Distributed</title>
+    <link rel="shortcut icon" type="image/x-icon" href="https://pytorch.org/favicon.ico?">
+
+    <style>
+        body {
+            margin: 0;
+            font-family:
+                -apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,
+                "Helvetica Neue",Arial,"Noto Sans",sans-serif,"Apple Color Emoji",
+                "Segoe UI Emoji","Segoe UI Symbol","Noto Color Emoji";
+            font-size: 1rem;
+            font-weight: 400;
+            line-height: 1.5;
+            color: #212529;
+            text-align: left;
+            background-color: #fff;
+        }
+        h1, h2, h2, h4, h5, h6, .h1, .h2, .h2, .h4, .h5, .h6 {
+            margin-bottom: .5rem;
+            font-weight: 500;
+            line-height: 1.2;
+        }
+        nav {
+            background-color: rgba(0, 0, 0, 0.17);
+            padding: 10px;
+            display: flex;
+            align-items: center;
+            padding: 16px;
+            justify-content: flex-start;
+        }
+        nav h1 {
+            display: inline-block;
+            margin: 0;
+        }
+        nav a {
+           margin: 0 8px;
+        }
+        section {
+            max-width: 1280px;
+            padding: 16px;
+            margin: 0 auto;
+        }
+        pre {
+            white-space: pre-wrap;
+            max-width: 100%;
+        }
+    </style>
+</head>
+
+<nav>
+    <h1>Torch Distributed Debug Server</h1>
+
+    <a href="/">Home</a>
+    <a href="/stacks">Python Stack Traces</a>
+    <a href="/fr_trace">FlightRecorder</a>
+    <a href="/fr_trace_nccl">FlightRecorder NCCL</a>
+    <a href="/profile">torch profiler</a>
+</nav>
+
+<section class="content">
+  {% block header %}{% endblock %}
+  {% for message in get_flashed_messages() %}
+    <div class="flash">{{ message }}</div>
+  {% endfor %}
+  {% block content %}{% endblock %}
+</section>
+    """,
+    "index.html": """
+{% extends "base.html" %}
+{% block header %}
+  <h1>{% block title %}Index{% endblock %}</h1>
+{% endblock %}
+{% block content %}
+Hi
+{% endblock %}
+    """,
+    "raw_resp.html": """
+{% extends "base.html" %}
+{% block header %}
+    <h1>{% block title %}{{title}}{% endblock %}</h1>
+{% endblock %}
+{% block content %}
+    {% for i, (addr, resp) in enumerate(zip(addrs, resps)) %}
+        <h2>Rank {{ i }}: {{ addr }}</h2>
+        {% if resp.status_code != 200 %}
+            <p>Failed to fetch: status={{ resp.status_code }}</p>
+            <pre>{{ resp.text }}</pre>
+        {% else %}
+            <pre>{{ resp.text }}</pre>
+        {% endif %}
+    {% endfor %}
+{% endblock %}
+    """,
+    "json_resp.html": """
+{% extends "base.html" %}
+{% block header %}
+    <h1>{% block title %}{{ title }}{% endblock %}</h1>
+{% endblock %}
+{% block content %}
+    {% for i, (addr, resp) in enumerate(zip(addrs, resps)) %}
+        <h2>Rank {{ i }}: {{ addr }}</h2>
+        {% if resp.status_code != 200 %}
+            <p>Failed to fetch: status={{ resp.status_code }}</p>
+            <pre>{{ resp.text }}</pre>
+        {% else %}
+            <pre>{{ format_json(resp.text) }}</pre>
+        {% endif %}
+    {% endfor %}
+{% endblock %}
+    """,
+    "profile.html": """
+{% extends "base.html" %}
+{% block header %}
+    <h1>{% block title %}torch.profiler{% endblock %}</h1>
+{% endblock %}
+
+{% block content %}
+    <form action="/profile" method="get">
+        <label for="duration">Duration (seconds):</label>
+        <input type="number" id="duration" name="duration" value="{{ duration }}" min="1" max="60">
+        <input type="submit" value="Submit">
+    </form>
+
+    <script>
+    function stringToArrayBuffer(str) {
+        const encoder = new TextEncoder();
+        return encoder.encode(str).buffer;
+    }
+    async function openPerfetto(data) {
+        const ui = window.open('https://ui.perfetto.dev/#!/');
+        if (!ui) { alert('Popup blocked. Allow popups for this page and click again.'); return; }
+
+        // Perfetto readiness handshake: PING until we receive PONG
+        await new Promise((resolve, reject) => {
+        const onMsg = (e) => {
+            if (e.source === ui && e.data === 'PONG') {
+            window.removeEventListener('message', onMsg);
+            clearInterval(pinger);
+            resolve();
+            }
+        };
+        window.addEventListener('message', onMsg);
+        const pinger = setInterval(() => { try { ui.postMessage('PING', '*'); } catch (_e) {} }, 250);
+        setTimeout(() => { clearInterval(pinger); window.removeEventListener('message', onMsg); reject(); }, 20000);
+        }).catch(() => { alert('Perfetto UI did not respond. Try again.'); return; });
+
+        ui.postMessage({
+        perfetto: {
+            buffer: stringToArrayBuffer(JSON.stringify(data)),
+            title: "torch profiler",
+            fileName: "trace.json",
+        }
+        }, '*');
+    }
+    </script>
+
+    {% for i, (addr, resp) in enumerate(zip(addrs, resps)) %}
+        <h2>Rank {{ i }}: {{ addr }}</h2>
+        {% if resp.status_code != 200 %}
+            <p>Failed to fetch: status={{ resp.status_code }}</p>
+            <pre>{{ resp.text }}</pre>
+        {% else %}
+            <script>
+            function run{{ i }}() {
+                var data = {{ resp.text | safe }};
+                openPerfetto(data);
+            }
+            </script>
+
+            <button onclick="run{{ i }}()">View {{ i }}</button>
+        {% endif %}
+    {% endfor %}
+{% endblock %}
+    """,
+}
+
+app = Flask(__name__)
+app.jinja_loader = DictLoader(templates)
+app.jinja_env.globals.update(
+    zip=zip,
+    format_json=format_json,
+    enumerate=enumerate,
+)
+
+
+@app.route("/")
+def _index_handler():
+    return render_template("index.html")
+
+
+@app.route("/stacks")
+def _stacks_handler():
+    addrs, resps = fetch_all("dump_traceback")
+    return render_template("raw_resp.html", title="Stacks", addrs=addrs, resps=resps)
+
+
+@app.route("/fr_trace")
+def _fr_trace_handler():
+    addrs, resps = fetch_all("fr_trace_json")
+
+    return render_template(
+        "json_resp.html",
+        title="FlightRecorder",
+        addrs=addrs,
+        resps=resps,
+    )
+
+
+@app.route("/fr_trace_nccl")
+def _fr_trace_nccl_handler():
+    addrs, resps = fetch_all("dump_nccl_trace_json", "onlyactive=true")
+
+    return render_template(
+        "json_resp.html",
+        title="FlightRecorder NCCL",
+        addrs=addrs,
+        resps=resps,
+    )
+
+
+@app.route("/profile")
+def _profiler_handler():
+    duration = request.args.get("duration", default=1.0, type=float)
+
+    addrs, resps = fetch_all("torch_profile", f"duration={duration}")
+
+    return render_template("profile.html", addrs=addrs, resps=resps)
+
+
+def main(port: int) -> None:
+    app.run(host="::", port=port)

torch/distributed/debug/_handlers.py

@@ -0,0 +1,22 @@
+import tempfile
+import time
+
+from torch._C._distributed_c10d import _register_handler, _Request, _Response
+from torch.profiler import _ExperimentalConfig, profile
+
+
+def _torch_profile(req: _Request, resp: _Response) -> None:
+    experimental_config = _ExperimentalConfig(
+        profile_all_threads=True,
+    )
+    duration = float(req.get_param("duration"))
+    with profile(record_shapes=True, experimental_config=experimental_config) as prof:
+        time.sleep(duration)
+
+    with tempfile.NamedTemporaryFile(prefix="torch_debug", suffix=".json") as f:
+        prof.export_chrome_trace(f.name)
+        resp.set_content(open(f.name, "rb").read(), "application/json")
+        resp.set_status(200)
+
+
+_register_handler("torch_profile", _torch_profile)

torch/distributed/debug/_store.py

@@ -0,0 +1,24 @@
+import os
+
+import torch.distributed as dist
+
+
+def get_rank() -> int:
+    return int(os.environ["RANK"])
+
+
+def get_world_size() -> int:
+    return int(os.environ["WORLD_SIZE"])
+
+
+def tcpstore_client() -> dist.Store:
+    MASTER_ADDR = os.environ["MASTER_ADDR"]
+    MASTER_PORT = int(os.environ["MASTER_PORT"])
+
+    store = dist.TCPStore(
+        host_name=MASTER_ADDR,
+        port=MASTER_PORT,
+        is_master=False,
+    )
+    store = dist.PrefixStore("debug_server", store)
+    return store