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benchmarks.md

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Benchmarks

Running

Benchmarks are implemented as binary rules in bazel, and can be either built and then run from the binary location in bazel-bin or run with bazel run, e.g.

bazel run -c opt opencensus/stats:stats_manager_benchmark [-- BENCHMARK_FLAGS]

Benchmarks use the Google benchmark library. This accepts several helpful flags, including

  • --benchmark_filter=REGEX: Run only benchmarks whose names match REGEX.
  • --benchmark_repetitions=N: Repeat each benchmark and calculate mean/median/stddev.
  • --benchmark_report_aggregates_only={true|false}: In conjunction with benchmark_repetitions, report only summary statistics and not single-run timings.

Don't forget to use -c opt to get an optimized build.

Profiling

Benchmarks can be profiled using the gperftools library. To install on Debian / Ubuntu:

sudo apt install google-perftools libgoogle-perftools-dev

When running the benchmark, set:

  • LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libprofiler.so.0 to enable the profiler.
  • CPUPROFILE=path_to_output_file
  • Optional: CPUPROFILE_FREQUENCY=4000 to increase resolution.
  • Optional: for visibility into inlined functions, build with -g1 or above.

Analyze the profile with google-pprof, which needs a path to the binary for symbolization.

Example:

bazel build -c opt --copt=-g1 opencensus/stats:stats_manager_benchmark
LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libprofiler.so.0 \
  CPUPROFILE=/tmp/prof \
  CPUPROFILE_FREQUENCY=4000 \
  ./bazel-bin/opencensus/stats/stats_manager_benchmark
google-pprof --web bazel-bin/opencensus/stats/stats_manager_benchmark /tmp/prof

google-pprof supports many analysis types - see its documentation for options.

Note that CPUPROFILE_FREQUENCY defaults to 100 samples per second. The maximum value libprofiler will accept is 4000. Most Linux kernels are built with CONFIG_HZ=250, so a single-threaded benchmark will produce at most 250 samples per second.