Metal backend: compute init/execute times

[manuelcandales]

This pull request introduces detailed performance tracking and reporting for the Metal backend, focusing on timing statistics for both initialization and execution phases. It adds infrastructure to collect, reset, and print timing data, and integrates statistics output into the Parakeet model example. Additionally, a preprocessor macro is defined to signal Metal backend availability.

Metal Backend Performance Statistics:

• Added timing statistics collection for init() and execute() calls in the Metal backend, including total time, call count, and per-method breakdowns. Accessor and reset functions are provided in stats.h and implemented in metal_backend.cpp.
• Introduced a new stats.cpp file with a function to print all collected Metal backend statistics, including per-method breakdowns for both initialization and execution.

Build and Integration Improvements:

• Added runtime/stats.cpp to the Metal backend build sources and defined the ET_BUILD_METAL preprocessor macro to indicate Metal backend support.

Example Model Enhancements:

• Updated the Parakeet example (main.cpp) to show Metal backend timing stats after model execution if Metal is enabled.

These changes provide better visibility into Metal backend performance and make it easier to profile and optimize model execution on Apple devices.

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/16639

• 📄 Preview Python docs built from this PR

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❌ 1 New Failure, 2 Unrelated Failures

As of commit 3cfefbf with merge base d58c8ee ():

NEW FAILURE - The following job has failed:

• Test CUDA Builds / test-model-cuda-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t 1ec5d087864ed692f9008e67efb951820c51bc6c8c36eb8b0d62226b7009910a /exec failed with exit code 1

BROKEN TRUNK - The following jobs failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / android / run-emulator (gh) (trunk failure)
  The process '/usr/bin/sh' failed with exit code 255
• pull / test-samsung-models-linux / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[Copilot]

Pull request overview

This PR adds timing instrumentation to the Metal backend for measuring initialization and execution performance, and exposes these statistics in the Parakeet example application.

Changes:

• Added timing measurement for Metal backend init() and execute() methods with per-method granularity
• Created a new stats API module with accessor and print functions for timing data
• Integrated Metal backend timing statistics into the Parakeet example to display performance metrics

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
backends/apple/metal/runtime/metal_backend.cpp	Added timing instrumentation using std::chrono to measure and track init/execute times in global variables
backends/apple/metal/runtime/stats.h	Defined public API for accessing Metal backend timing statistics
backends/apple/metal/runtime/stats.cpp	Implemented function to print formatted timing statistics to stdout
backends/apple/metal/CMakeLists.txt	Added stats.cpp to build and defined ET_BUILD_METAL preprocessor macro
examples/models/parakeet/main.cpp	Added performance statistics output section that calls Metal backend stats when built with Metal support

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

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