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diff --git a/docs/performance/perfstats.md b/docs/performance/perfstats.md new file mode 100644 index 0000000000..6ffaa55da9 --- /dev/null +++ b/docs/performance/perfstats.md @@ -0,0 +1,30 @@ +# PerfStats + +PerfStats is a framework for the low-overhead selective collection of internal performance metrics. +The results are accessible through ChromeUtils, Browsertime output, and in select performance tests. + +## Adding a new PerfStat +Define the new PerfStat by adding it to [this list](https://searchfox.org/mozilla-central/rev/b1e5f2c7c96be36974262551978d54f457db2cae/tools/performance/PerfStats.h#34-53) in [`PerfStats.h`](https://searchfox.org/mozilla-central/rev/52da19becaa3805e7f64088e91e9dade7dec43c8/tools/performance/PerfStats.h). +Then, in C++ code, wrap execution in an RAII object, e.g. +``` +PerfStats::AutoMetricRecording<PerfStats::Metric::MyMetric>() +``` +or call the following function manually: +``` +PerfStats::RecordMeasurement(PerfStats::Metric::MyMetric, Start, End) +``` +For incrementing counters, use the following: +``` +PerfStats::RecordMeasurementCount(PerfStats::Metric::MyMetric, incrementCount) +``` + +[Here's an example of a patch where a new PerfStat was added and used.](https://hg.mozilla.org/mozilla-central/rev/3e85a73d1fa5c816fdaead66ecee603b38f9b725) + +## Enabling collection +To enable collection, use `ChromeUtils.SetPerfStatsCollectionMask(MetricMask mask)`, where `mask=0` disables all metrics and `mask=0xFFFFFFFF` enables all of them. +`MetricMask` is a bitmask based on `Metric`, i.e. `Metric::LayerBuilding (2)` is synonymous to `1 << 2` in `MetricMask`. + +## Accessing results +Results can be accessed with `ChromeUtils.CollectPerfStats()`. +The Browsertime test framework will sum results across processes and report them in its output. +The raptor-browsertime Windows essential pageload tests also collect all PerfStats. |