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