3e1b99498f
Bug: 313526654 Change-Id: Iab8b2915c0627f5830344cb8145810f7898b5409 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5337346 Reviewed-by: David Benjamin <davidben@chromium.org> Auto-Submit: Daniel Cheng <dcheng@chromium.org> Commit-Queue: Daniel Cheng <dcheng@chromium.org> Cr-Commit-Position: refs/heads/main@{#1267454}
114 lines
4.0 KiB
Markdown
114 lines
4.0 KiB
Markdown
# Linux Profiling
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How to profile Chromium on Linux.
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See
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[Profiling Chromium and WebKit](https://sites.google.com/a/chromium.org/dev/developers/profiling-chromium-and-webkit)
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for alternative discussion.
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## CPU Profiling
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gprof: reported not to work (taking an hour to load on our large binary).
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oprofile: Dean uses it, says it's good. (As of 9/16/9 oprofile only supports
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timers on the new Z600 boxes, which doesn't give good granularity for profiling
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startup).
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TODO(willchan): Talk more about oprofile, gprof, etc.
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Also see
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https://sites.google.com/a/chromium.org/dev/developers/profiling-chromium-and-webkit
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### perf
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`perf` is the successor to `oprofile`. It's maintained in the kernel tree, it's
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available on Ubuntu in the package `linux-tools`.
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To capture data, you use `perf record`. Some examples:
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```shell
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# captures the full execution of the program
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perf record -f -g out/Release/chrome
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# captures a particular pid, you can start at the right time, and stop with
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# ctrl-C
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perf record -f -g -p 1234
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perf record -f -g -a # captures the whole system
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```
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> ⚠️ Note: on virtualized systems, e.g. cloudtops, the PMU counters may not
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be available or may be broken. Use `-e cpu-clock` as a workaround.
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Googlers, see [b/313526654](https://b.corp.google.com/issues/313526654).
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Some versions of the perf command can be confused by process renames. Affected
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versions will be unable to resolve Chromium's symbols if it was started through
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perf, as in the first example above. It should work correctly if you attach to
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an existing Chromium process as shown in the second example. (This is known to
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be broken as late as 3.2.5 and fixed as early as 3.11.rc3.g36f571. The actual
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affected range is likely much smaller. You can download and build your own perf
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from source.)
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The last one is useful on limited systems with few cores and low memory
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bandwidth, where the CPU cycles are shared between several processes (e.g.
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chrome browser, renderer, plugin, X, pulseaudio, etc.)
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To look at the data, you use:
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perf report
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This will use the previously captured data (`perf.data`).
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## Heap Profiling
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#### Dumping a profile of a running process
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To programmatically generate a heap profile before exit, you can use gdb to
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attach at any point:
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1. Attach gdb to the process: `$ gdb -p 12345`
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2. Cause it to dump a profile: `(gdb) p HeapProfilerDump("foobar")`
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3. The filename will be printed on the console you started Chrome from; e.g.
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"`Dumping heap profile to heap.0001.heap (foobar)`"
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#### Analyzing dumps
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You can then analyze dumps using the `pprof` script (distributed with
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google-perftools, installed by default on Googler Linux workstations; on Ubuntu
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it is called `google-pprof`). For example:
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pprof --gv out/Release/chrome /tmp/heapprofile
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This will generate a visual representation of the heap profile as a postscript
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file and load it up using `gv`. For more powerful commands, please refer to the
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pprof help output and the google-perftools documentation.
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(pprof is slow. Googlers can try the not-open-source cpprof; Evan wrote an open
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source alternative [available on github](https://github.com/martine/hp).)
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#### Sandbox
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Sandboxed renderer subprocesses will fail to write out heap profiling dumps. To
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work around this, turn off the sandbox (via `export CHROME_DEVEL_SANDBOX=`).
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#### More reading
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For further information, please refer to
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http://google-perftools.googlecode.com/svn/trunk/doc/heapprofile.html.
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## Paint profiling
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You can use Xephyr to profile how chrome repaints the screen. Xephyr is a
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virtual X server like Xnest with debugging options which draws red rectangles to
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where applications are drawing before drawing the actual information.
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export XEPHYR_PAUSE=10000
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Xephyr :1 -ac -screen 800x600 &
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DISPLAY=:1 out/Debug/chrome
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When ready to start debugging issue the following command, which will tell
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Xephyr to start drawing red rectangles:
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kill -USR1 `pidof Xephyr`
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For further information, please refer to
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http://cgit.freedesktop.org/xorg/xserver/tree/hw/kdrive/ephyr/README.
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