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99 lines
3.7 KiB
Markdown
99 lines
3.7 KiB
Markdown
# Benchmarking
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## Debug Builds
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Debug builds (\--enable-debug) and non-optimized builds
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(\--disable-optimize) are *much* slower. Any performance metrics
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gathered by such builds are largely unrelated to what would be found in
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a release browser.
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## Rust optimization level
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Local optimized builds are [compiled with rust optimization level 1 by
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default](https://groups.google.com/forum/#!topic/mozilla.dev.platform/pN9O5EB_1q4),
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unlike Nightly builds, which use rust optimization level 2. This setting
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reduces build times significantly but comes with a serious hit to
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runtime performance for any rust code ([for example stylo and
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webrender](https://groups.google.com/d/msg/mozilla.dev.platform/pN9O5EB_1q4/ooXNuqMECAAJ)).
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Add the following to your [mozconfig] in order to build with level 2:
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```
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ac_add_options RUSTC_OPT_LEVEL=2
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```
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## Profile Guided Optimization (PGO)
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[Profile Guided
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Optimization](/build/buildsystem/pgo.rst#profile-guided-optimization) is
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disabled by default and may improve runtime by up to 20%. However, it takes a
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long time to build. To enable, add the following to your [mozconfig]:
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```
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ac_add_options MOZ_PGO=1
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```
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## GC Poisoning
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Many Firefox builds have a diagnostic tool that causes crashes to happen
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sooner and produce much more actionable information, but also slow down
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regular usage substantially. In particular, \"GC poisoning\" is used in
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all debug builds, and in optimized Nightly builds (but not opt Developer
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Edition or Beta builds). The poisoning can be disabled by setting the
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environment variable
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```
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JSGC_DISABLE_POISONING=1
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```
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before starting the browser.
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## Async Stacks
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Async stacks no longer impact performance since **Firefox 78**, as
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{{bug(1601179)}} limits async stack capturing to when DevTools is
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opened.
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Another option that is on by default in non-release builds is the
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preference javascript.options.asyncstack, which provides better
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debugging information to developers. Set it to false to match a release
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build. (This may be disabled for many situations in the future. See
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{{bug(1280819)}}.
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## Accelerated Graphics
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Especially on Linux, accelerated graphics can sometimes lead to severe
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performance problems even if things look ok visually. Normally you would
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want to leave acceleration enabled while profiling, but on Linux you may
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wish to disable accelerated graphics (Preferences -\> Advanced -\>
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General -\> Use hardware acceleration when available).
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## Flash Plugin
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If you are profiling real websites, you should disable the Adobe Flash
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plugin so you are testing Firefox code and not Flash jank problems. In
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about:addons \> Plugins, set Shockwave Flash to \"Never Activate\".
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## Timer Precision
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Firefox reduces the precision of the Performance APIs and other clock
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and timer APIs accessible to Web Content. They are currently reduce to a
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multiple of 2ms; which is controlled by the privacy.reduceTimerPrecision
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about:config flag.
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The exact value of the precision is controlled by the
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privacy.resistFingerprinting.reduceTimerPrecision.microseconds
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about:config flag.
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## Profiling tools
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Currently the Gecko Profiler has limitations in the UI for inverted call
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stack top function analysis which is very useful for finding heavy
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functions that call into a whole bunch of code. Currently such functions
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may be easy to miss looking at a profile, so feel free to *also* use
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your favorite native profiler. It also lacks features such as
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instruction level profiling which can be helpful in low level profiling,
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or finding the hot loop inside a large function, etc. Some example tools
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include Instruments on OSX (part of XCode), [RotateRight
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Zoom](http://www.rotateright.com/) on Linux (uses perf underneath), and
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Intel VTune on Windows or Linux.
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[mozconfig]: /setup/configuring_build_options.rst#using-a-mozconfig-configuration-file
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