Built-In Tools

For JavaScript issues, the built in profiler works very well.  To use this open up the Chrome Dev Tools (right click, Inspect Element) and select the 'Profiles' tab.

For a broader understanding of Chromium speed and bottlenecks, as well as understanding how posted-task and threads interact in aggregate, there is a cross-platform, task-level profiler built in.  Profiler results can be seen in about:profiler (or equivalently chrome://profiler)  For more details, visit  (http://www.chromium.org/developers/threaded-task-tracking).

See chrome://tracing for timelines showing TRACE_EVENT activity across all the different threads; originally used for GPU performance, and will probably require you to add TRACE_EVENT calls to the features you're interested in outside of compositing & rendering (this was named about://gpu through M14).

For native C++ code the tools depend on the OS.

Note that basic printf debugging and using a general debugger (such as gdb) may be sufficient for some purposes. However, more specialized tools are available.

• Add profiling=1 release_extra_cflags=-fno-omit-frame-pointer disable_pie=1 to your GYP_DEFINES then rerun gyp (build/gyp_chromium) and rebuild. This will ensure that even your Release builds will have the necessary flags to be able to capture callstacks. Assuming you already have a GYP_DEFINES line in your configuration file, adding the following line after it should work:

• Chromium will accept three new command line flags:
• --profiling-file
  This is a template for where the pprof data gets generated. It can contain the substrings {pid} and {count} which will be replaced by the pid of the process and the count of the profile run w/in a process. Chromium also adds a {type} substring replacement for the process type. The default is chrome-profile-{type}-{pid}
• --profiling-at-start
  When specified profiling will be enabled from the very beginning of the program. An optional string argument can be given which can specify a process type to profile (e.g., zygote, renderer). This works for the renderer (--profiling-at-start=renderer) as well if you also add --no-sandbox, so that the samples can be written out to disk.
• --profiling-flush
  This causes the profile data to be flushed periodically. Typically this isn't needed as the data is flushed at exit, but sometimes there are bugs that prevent the atexit handlers from getting run. This is more often the case when --single-process is specified. It's also useful when profiling the renderer, as the renderer is more likely to be terminated quickly.
• The perf data is generated by default in the current directory, so to avoid making a mess of the source tree, it's safest to run Chromium from outside the source directory, such as via:

src/out/Release/chrome

• You can turn profiling on and off:
• ...from within the program by using the chrome/common/Profiling class;
• ...interactively via a new menu item (checkbox), Menu→Tools→Profiling Enabled.
• Only the browser process (Chromium) is profiled. To profile the renderer (Blink), run in single-process mode via:

pprof

test_shell

• Compile test_shell with profiling enabled (same as above)
• Run test_shell without the CPUPROFILE environment variable set and pass in the --profiler flag (for example, "out/Release/test_shell --profiler"
• Start the profile by running "(new chromium.Profiler).start()", stop it by running "(new chromium.Profiler).stop()".  This can be done from JavaScript inside the page or by typing "javascript:(new chromium.Profiler).start()" into the URL bar and hitting enter

perf

Profiling for Chrome OS is very similar to Linux, with a couple of key differences

OS X

Windows

AMD Code Analyst is a free profiler that can run inside Visual Studio. It captures frequency counts for functions in every process on the computer. It can optionally capture call-stack information, %CPU, and memory usage statistics; even with the Frame Pointer Omission optimization turned off (build\internal\release_defaults.gypi; under 'VCCLCompilerTool' set 'OmitFramePointers':'false'?), the call stack capture can have lots of bad information, but at least the most-frequent-caller seems accurate in practice.

Intel's VTune 9.1 does work in the Sampling mode (using the hardware performance counters), but call graphs are unavailable in Windows 7/64.  Note also that drilling down into the results for chrome.dll is extremely slow (on the order of many minutes) and may appear hung.  It does work (I suggest coffee or foosball).  VTune has been essentially supplanted by Intel® VTune™ Amplifier XE, which is an entirely new code base and interface, AFAIK.

Very Sleepy (http://www.codersnotes.com/sleepy) is a light-weight standalone profiler that seems to works pretty well for casual use and offers a decent set of features.

Both nVidia PerfHUD and Microsoft PIX are freely available. They may not run without making minor changes to how the graphics contexts are set up; check with the chrome-gpu team for current details.

The OpenGL Profiler for OSX allows real-time inspection of the top GL performance bottlenecks, as well as call traces.  In order to use it with Chrome/Mac, you must pass --disable-gpu-sandbox on the command line.  Some people have had more luck attaching it to the GPU process after-the-fact than launching Chrome from within the Profiler; YMMV.

GPUView is a Windows tool that utilizes ETW (Event Tracing for Windows) for visualizing low-level GPU, driver and kernel interactions in a time-based viewer.  It's available as part of the Microsoft Windows Performance Toolkit, in  %ProgramFiles%\Microsoft Windows Performance Toolkit\GPUView.  There's a README.TXT in there with basic instructions, or see http://graphics.stanford.edu/~mdfisher/GPUView.html.  N.B.:  There's a known bug which causes GPUView to crash when visualizing traces captured on machines with more than 8 cores.  On an HP Z600, disabling hyperthreading in the BIOS is enough to work around this issue.