andybons 6e0cd21569 [Docs] Add wiki content to Markdown docs

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BUG=none
R=hablich@chromium.org

Review URL: https://codereview.chromium.org/1347153006

Cr-Commit-Position: refs/heads/master@{#30972}

2015-09-28 12:41:25 +00:00

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Introduction

V8's CPU & Heap profilers are trivial to use from V8's shells (see V8Profiler), but it may appear confusing how to use them with Chromium. This page should help you with it.

Instructions

Why using V8's profilers with Chromium is different from using them with V8 shells?

Chromium is a complex application, unlike V8 shells. Below is the list of Chromium features that affect profiler usage:

each renderer is a separate process (OK, not actually each, but let's omit this detail), so they can't share the same log file;
sandbox built around renderer process prevents it from writing to a disk;
Developer Tools configure profilers for their own purposes;
V8's logging code contains some optimizations to simplify logging state checks.

So, how to run Chromium to get a CPU profile?

Here is how to run Chromium in order to get a CPU profile from the start of the process:

./Chromium --no-sandbox --js-flags="--logfile=%t.log --prof"

Please note that you wouldn't see profiles in Developer Tools, because all the data is being logged to a file, not to Developer Tools.

Flags description

--no-sandbox - turns off the renderer sandbox, obviously must have;
--js-flags - this is the containers for flags passed to V8:
- --logfile=%t.log - specifies a name pattern for log files; %t gets expanded into current time in milliseconds, so each process gets its own log file; you can use prefixes and suffixes if you want, like this: prefix-%t-suffix.log;
- --prof - tells V8 to write statistical profiling information into the log file.

Notes

Under Windows, be sure to turn on .MAP file creation for chrome.dll, but not for chrome.exe.

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