30 lines
1.6 KiB
Markdown
30 lines
1.6 KiB
Markdown
# PerfStats
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PerfStats is a framework for the low-overhead selective collection of internal performance metrics.
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The results are accessible through ChromeUtils, Browsertime output, and in select performance tests.
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## Adding a new PerfStat
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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).
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Then, in C++ code, wrap execution in an RAII object, e.g.
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```
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PerfStats::AutoMetricRecording<PerfStats::Metric::MyMetric>()
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```
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or call the following function manually:
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```
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PerfStats::RecordMeasurement(PerfStats::Metric::MyMetric, Start, End)
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```
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For incrementing counters, use the following:
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```
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PerfStats::RecordMeasurementCount(PerfStats::Metric::MyMetric, incrementCount)
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```
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[Here's an example of a patch where a new PerfStat was added and used.](https://hg.mozilla.org/mozilla-central/rev/3e85a73d1fa5c816fdaead66ecee603b38f9b725)
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## Enabling collection
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To enable collection, use `ChromeUtils.SetPerfStatsCollectionMask(MetricMask mask)`, where `mask=0` disables all metrics and `mask=0xFFFFFFFF` enables all of them.
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`MetricMask` is a bitmask based on `Metric`, i.e. `Metric::LayerBuilding (2)` is synonymous to `1 << 2` in `MetricMask`.
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## Accessing results
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Results can be accessed with `ChromeUtils.CollectPerfStats()`.
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The Browsertime test framework will sum results across processes and report them in its output.
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The raptor-browsertime Windows essential pageload tests also collect all PerfStats.
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