[MPS] Add API to query GPU core count (#160414)

Using good old IOKit to get `gpu-core-count` property from device implementing `AGXAccelerator` service
Expose this one as `torch.backend.mps.get_core_count()` and make it accessible via `MpsInterface` to the inductor

Test Plan: Run `python3 -c "import torch;print(torch.backends.mps.get_name(), torch.backends.mps.get_core_count())"` and compare it to `system_profiler SPDisplaysDataType|head -n10`
```
% python3 -c "import torch;print(torch.backends.mps.get_name(), torch.backends.mps.get_core_count())"
Apple M1 Pro 16
% system_profiler SPDisplaysDataType|head -n10
Graphics/Displays:

    Apple M1 Pro:

      Chipset Model: Apple M1 Pro
      Type: GPU
      Bus: Built-In
      Total Number of Cores: 16
      Vendor: Apple (0x106b)
      Metal Support: Metal 3
```

This would significantly improve occupancy for torch.compile generated kernels

Pull Request resolved: https://github.com/pytorch/pytorch/pull/160414
Approved by: https://github.com/dcci

CMakeLists.txt

@@ -1196,7 +1196,7 @@ if(APPLE)
     string(
       APPEND
       CMAKE_SHARED_LINKER_FLAGS
-      " -weak_framework Foundation -weak_framework MetalPerformanceShaders -weak_framework MetalPerformanceShadersGraph -weak_framework Metal"
+      " -weak_framework Foundation -weak_framework MetalPerformanceShaders -weak_framework MetalPerformanceShadersGraph -weak_framework Metal -weak_framework IOKit"
     )
     # To suppress MPSGraph availability warnings
     append_cxx_flag_if_supported("-Wno-unguarded-availability-new"

aten/src/ATen/mps/MPSDevice.h

@@ -55,6 +55,17 @@ class TORCH_API MPSDevice {
    */
   bool isMacOS13Plus(MacOSVersion version) const;
 
+  /**
+   * Returns device name
+   */
+  std::string getName() const;
+
+  /**
+   * Returns number of GPU cores.
+   * 1 Core = 16 ExecutionUnit x 8 ALU x 24 threads
+   */
+  unsigned getCoreCount() const;
+
   ~MPSDevice();
 
  private:

aten/src/ATen/mps/MPSDevice.mm

@@ -85,10 +85,36 @@ bool MPSDevice::isMacOS13Plus(MacOSVersion version) const {
   }
 }
 
+std::string MPSDevice::getName() const {
+  @autoreleasepool {
+    return [[_mtl_device name] UTF8String];
+  }
+}
+
+unsigned MPSDevice::getCoreCount() const {
+  io_iterator_t iterator = 0;
+  io_registry_entry_t entry = 0;
+  int core_count = 0;
+  auto matchingDict = IOServiceMatching("AGXAccelerator");
+  TORCH_INTERNAL_ASSERT(matchingDict, "Failed to create matching dict");
+  const auto status = IOServiceGetMatchingServices(kIOMainPortDefault, matchingDict, &iterator);
+  TORCH_INTERNAL_ASSERT(status == KERN_SUCCESS);
+  while ((entry = IOIteratorNext(iterator)) != 0) {
+    auto property = IORegistryEntryCreateCFProperty(entry, CFSTR("gpu-core-count"), kCFAllocatorDefault, 0);
+    auto found = CFNumberGetValue(static_cast<CFNumberRef>(property), kCFNumberIntType, &core_count);
+    CFRelease(property);
+    IOObjectRelease(entry);
+    if (found) {
+      break;
+    }
+  }
+  IOObjectRelease(iterator);
+  return core_count;
+}
+
 at::Allocator* GetMPSAllocator(bool useSharedAllocator) {
   return getIMPSAllocator(useSharedAllocator);
 }
-
 bool is_available() {
   return MPSDevice::getInstance()->device() != nil;
 }

torch/_C/__init__.pyi.in

@@ -1979,7 +1979,9 @@ def _mtia_resetPeakMemoryStats(device: _int) -> None: ...
 
 # Defined in torch/csrc/mps/Module.cpp
 def _mps_deviceSynchronize() -> None: ...
+def _mps_get_core_count() -> _int: ...
 def _mps_get_default_generator() -> Generator: ...
+def _mps_get_name() -> _str: ...
 def _mps_emptyCache() -> None: ...
 def _mps_setMemoryFraction(fraction: _float) -> None: ...
 def _mps_currentAllocatedMemory() -> _int: ...

torch/_dynamo/device_interface.py

@@ -17,6 +17,7 @@ specialized implementations for each hardware backend's unique features.
 
 import inspect
 import time
+from collections import namedtuple
 from collections.abc import Iterable
 from dataclasses import dataclass
 from typing import Any, Callable, Literal, Optional, Union
@@ -544,8 +545,10 @@ class MpsInterface(DeviceInterface):
 
     class Worker:
         @staticmethod
-        def get_device_properties(device: torch.types.Device = None) -> dict[str, Any]:
-            return {}
+        def get_device_properties(device: torch.types.Device = None) -> Any:
+            return namedtuple("MPSProperties", ["multi_processor_count"])(
+                torch.backends.mps.get_core_count()  # type: ignore[arg-type]
+            )
 
         @staticmethod
         def current_device() -> int:

torch/_inductor/runtime/hints.py

@@ -153,9 +153,6 @@ class DeviceProperties(typing.NamedTuple):
         except AttributeError:
             if device_type == "xpu":
                 multi_processor_count = props.gpu_subslice_count
-            elif device_type == "mps":
-                # TODO: Fetch the actual value from ioreg
-                multi_processor_count = 8
             elif device_type == "mtia":
                 multi_processor_count = 64
             else:

torch/backends/mps/__init__.py

@@ -5,7 +5,14 @@ import torch
 from torch.library import Library as _Library
 
 
-__all__ = ["is_built", "is_available", "is_macos13_or_newer", "is_macos_or_newer"]
+__all__ = [
+    "get_core_count",
+    "get_name",
+    "is_built",
+    "is_available",
+    "is_macos13_or_newer",
+    "is_macos_or_newer",
+]
 
 
 def is_built() -> bool:
@@ -36,6 +43,23 @@ def is_macos13_or_newer(minor: int = 0) -> bool:
     return torch._C._mps_is_on_macos_or_newer(13, minor)
 
 
+@_lru_cache
+def get_name() -> str:
+    r"""Return Metal device name"""
+    return torch._C._mps_get_name()
+
+
+@_lru_cache
+def get_core_count() -> int:
+    r"""Return GPU core count.
+
+    According to the documentation, one core is comprised of 16 Execution Units.
+    One execution Unit has 8 ALUs.
+    And one ALU can run 24 threads, i.e. one core is capable of executing 3072 threads concurrently.
+    """
+    return torch._C._mps_get_core_count()
+
+
 _lib: Optional[_Library] = None
 
 

torch/csrc/Module.cpp

@@ -20,7 +20,6 @@
 #include <ATen/Parallel.h>
 #include <ATen/Utils.h>
 #include <ATen/core/Vitals.h>
-#include <ATen/detail/AcceleratorHooksInterface.h>
 #include <ATen/dlpack.h>
 #include <ATen/native/ConvUtils.h>
 #include <ATen/native/ForeachUtils.h>

torch/csrc/mps/Module.cpp

@@ -501,6 +501,12 @@ void initModule(PyObject* module) {
     at::mps::getMPSProfiler().startCapture(fileName);
   });
   m.def("_mps_stopCapture", []() { at::mps::getMPSProfiler().stopCapture(); });
+  m.def("_mps_get_name", []() {
+    return at::mps::MPSDevice::getInstance()->getName();
+  });
+  m.def("_mps_get_core_count", []() {
+    return at::mps::MPSDevice::getInstance()->getCoreCount();
+  });
 }
 #endif /* USE_MPS */