mirror of
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398a8ac2e8
* Build libpfm as a dependency to allow collection of perf counters
This commit builds libpfm using rules_foreign_cc and lets the default
build of the benchmark library support perf counter collection without
needing additional work from users.
Tested with a custom target:
```
bazel run \
--override_repository=com_github_google_benchmark=/home/raghu/benchmark \
-c opt :test-bench -- "--benchmark_perf_counters=INSTRUCTIONS,CYCLES"
Using profile: local
<snip>
----------------------------------------------------------------------
Benchmark Time CPU Iterations UserCounters...
----------------------------------------------------------------------
BM_Test 0.279 ns 0.279 ns 1000000000 CYCLES=1.00888 INSTRUCTIONS=2
```
Signed-off-by: Raghu Raja <raghu@enfabrica.net>
* Adding myself to the CONTRIBUTORS file per CLA guidance
Enfabrica has already signed a corporate CLA.
Signed-off-by: Raghu Raja <raghu@enfabrica.net>
Signed-off-by: Raghu Raja <raghu@enfabrica.net>
36 lines
1.5 KiB
Markdown
36 lines
1.5 KiB
Markdown
<a name="perf-counters" />
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# User-Requested Performance Counters
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When running benchmarks, the user may choose to request collection of
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performance counters. This may be useful in investigation scenarios - narrowing
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down the cause of a regression; or verifying that the underlying cause of a
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performance improvement matches expectations.
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This feature is available if:
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* The benchmark is run on an architecture featuring a Performance Monitoring
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Unit (PMU),
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* The benchmark is compiled with support for collecting counters. Currently,
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this requires [libpfm](http://perfmon2.sourceforge.net/), which is built as a
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dependency via Bazel.
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The feature does not require modifying benchmark code. Counter collection is
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handled at the boundaries where timer collection is also handled.
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To opt-in:
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* If using a Bazel build, add `--define pfm=1` to your buid flags
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* If using CMake:
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* Install `libpfm4-dev`, e.g. `apt-get install libpfm4-dev`.
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* Enable the CMake flag `BENCHMARK_ENABLE_LIBPFM` in `CMakeLists.txt`.
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To use, pass a comma-separated list of counter names through the
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`--benchmark_perf_counters` flag. The names are decoded through libpfm - meaning,
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they are platform specific, but some (e.g. `CYCLES` or `INSTRUCTIONS`) are
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mapped by libpfm to platform-specifics - see libpfm
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[documentation](http://perfmon2.sourceforge.net/docs.html) for more details.
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The counter values are reported back through the [User Counters](../README.md#custom-counters)
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mechanism, meaning, they are available in all the formats (e.g. JSON) supported
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by User Counters.
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