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MPS Environment Variables

PyTorch Environment Variables

Variable Description
PYTORCH_DEBUG_MPS_ALLOCATOR If set to 1, set allocator logging level to verbose.
PYTORCH_MPS_LOG_PROFILE_INFO Set log options bitmask to MPSProfiler. See LogOptions enum in aten/src/ATen/mps/MPSProfiler.h for available options.
PYTORCH_MPS_TRACE_SIGNPOSTS Set profile and signpost bitmasks to MPSProfiler. See ProfileOptions and SignpostTypes enums in aten/src/ATen/mps/MPSProfiler.h for available options.
PYTORCH_MPS_HIGH_WATERMARK_RATIO High watermark ratio for MPS allocator. By default, it is set to 1.7.
PYTORCH_MPS_LOW_WATERMARK_RATIO Low watermark ratio for MPS allocator. By default, it is set to 1.4 if the memory is unified and set to 1.0 if the memory is discrete.
PYTORCH_MPS_FAST_MATH If set to 1, enable fast math for MPS metal kernels. See section 1.6.3 in https://developer.apple.com/metal/Metal-Shading-Language-Specification.pdf for precision implications.
PYTORCH_MPS_PREFER_METAL If set to 1, force using metal kernels instead of using MPS Graph APIs. For now this is only used for matmul op.
PYTORCH_ENABLE_MPS_FALLBACK If set to 1, full back operations to CPU when MPS does not support them.

Note

high watermark ratio is a hard limit for the total allowed allocations

  • 0.0 : disables high watermark limit (may cause system failure if system-wide OOM occurs)
  • 1.0 : recommended maximum allocation size (i.e., device.recommendedMaxWorkingSetSize)
  • >1.0: allows limits beyond the device.recommendedMaxWorkingSetSize

e.g., value 0.95 means we allocate up to 95% of recommended maximum allocation size; beyond that, the allocations would fail with OOM error.

low watermark ratio is a soft limit to attempt limiting memory allocations up to the lower watermark level by garbage collection or committing command buffers more frequently (a.k.a, adaptive commit). Value between 0 to m_high_watermark_ratio (setting 0.0 disables adaptive commit and garbage collection) e.g., value 0.9 means we 'attempt' to limit allocations up to 90% of recommended maximum allocation size.