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diff --git a/third-party/benchmark/docs/perf_counters.md b/third-party/benchmark/docs/perf_counters.md new file mode 100644 index 000000000000..74560e966971 --- /dev/null +++ b/third-party/benchmark/docs/perf_counters.md @@ -0,0 +1,34 @@ +<a name="perf-counters" /> + +# User-Requested Performance Counters + +When running benchmarks, the user may choose to request collection of +performance counters. This may be useful in investigation scenarios - narrowing +down the cause of a regression; or verifying that the underlying cause of a +performance improvement matches expectations. + +This feature is available if: + +* The benchmark is run on an architecture featuring a Performance Monitoring + Unit (PMU), +* The benchmark is compiled with support for collecting counters. Currently, + this requires [libpfm](http://perfmon2.sourceforge.net/) be available at build + time + +The feature does not require modifying benchmark code. Counter collection is +handled at the boundaries where timer collection is also handled. + +To opt-in: + +* Install `libpfm4-dev`, e.g. `apt-get install libpfm4-dev`. +* Enable the cmake flag BENCHMARK_ENABLE_LIBPFM. + +To use, pass a comma-separated list of counter names through the +`--benchmark_perf_counters` flag. The names are decoded through libpfm - meaning, +they are platform specific, but some (e.g. `CYCLES` or `INSTRUCTIONS`) are +mapped by libpfm to platform-specifics - see libpfm +[documentation](http://perfmon2.sourceforge.net/docs.html) for more details. + +The counter values are reported back through the [User Counters](../README.md#custom-counters) +mechanism, meaning, they are available in all the formats (e.g. JSON) supported +by User Counters.
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