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dawn-cmake/docs/testing.md

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Testing Dawn

(TODO)

Dawn Perf Tests

For benchmarking with dawn_perf_tests, it's best to build inside a Chromium checkout using the following GN args:

is_official_build = true  # Enables highest optimization level, using LTO on some platforms
use_dawn = true           # Required to build Dawn
use_cfi_icall=false       # Required because Dawn dynamically loads function pointers, and we don't sanitize them yet.

Terminology

  • Iteration: The unit of work being measured. It could be a frame, a draw call, a data upload, a computation, etc. dawn_perf_tests metrics are reported as time per iteration.
  • Step: A group of Iterations run together. The number of iterationsPerStep is provided to the constructor of DawnPerfTestBase.
  • Trial: A group of Steps run consecutively. kNumTrials are run for each test. A Step in a Trial is run repetitively for approximately kCalibrationRunTimeSeconds. Metrics are accumlated per-trial and reported as the total time divided by numSteps * iterationsPerStep. maxStepsInFlight is passed to the DawnPerfTestsBase constructor to limit the number of Steps pipelined.

(See //src/tests/perf_tests/DawnPerfTest.h for the values of the constants).

Metrics

dawn_perf_tests measures the following metrics:

  • wall_time: The time per iteration, including time waiting for the GPU between Steps in a Trial.
  • cpu_time: The time per iteration, not including time waiting for the GPU between Steps in a Trial.
  • validation_time: The time for CommandBuffer / RenderBundle validation.
  • recording_time: The time to convert Dawn commands to native commands.

Metrics are reported according to the format specified at [chromium]//build/scripts/slave/performance_log_processor.py

Dumping Trace Files

The test harness supports a --trace-file=path/to/trace.json argument where Dawn trace events can be dumped. The traces can be viewed in Chrome's about://tracing viewer.

Test Runner

//scripts/perf_test_runner.py may be run to continuously run a test and report mean times and variances.

Currently the script looks in the out/Release build directory and measures the wall_time metric (hardcoded into the script). These should eventually become arguments.

Example usage:

scripts/perf_test_runner.py DrawCallPerf.Run/Vulkan__e_skip_validation

Tests

BufferUploadPerf

Tests repetitively uploading data to the GPU using either SetSubData or CreateBufferMapped.

DrawCallPerf

DrawCallPerf tests drawing a simple triangle with many ways of encoding commands, binding, and uploading data to the GPU. The rationale for this is the following:

  • Static/Multiple/Dynamic vertex buffers: Tests switching buffer bindings. This has a state tracking cost as well as a GPU driver cost.
  • Static/Multiple/Dynamic bind groups: Same rationale as vertex buffers
  • Static/Dynamic pipelines: In addition to a change to GPU state, changing the pipeline layout incurs additional state tracking costs in Dawn.
  • With/Without render bundles: All of the above can have lower validation costs if precomputed in a render bundle.
  • Static/Dynamic data: Updating data for each draw is a common use case. It also tests the efficiency of resource transitions.