Using SlowCalls

Getting a tree with instrumentation

First, you need to get a tree containing Javascript instrumentation that is fully working. (bug 507012 added the instrumentation, but it keeps getting perturbed by JS engine changes, so that it ends up getting mismatched JS function enters/exits.)

Option 1: mozilla-central

The current (2010-Oct-11) m-c tree's JS interpreter is in an intermediate state that I can't get the instrumentation working for. So my current workaround is to do a wholesale update to a fairly recent tracemonkey and then add some patches that fix the instrumentation there.

I boiled it down into 3 ugly patches:

• switch to tracemonkey: hg qimport 'http://people.mozilla.org/~sfink/slowcalls-proto/import-tracemonkey'
• apply instrumentation fixes + a bunch of other irrelevant crud that I had lying around: hg qimport 'http://people.mozilla.org/~sfink/slowcalls-proto/profiling-megapatch'
• add an instrumentation client that just logs everything to a filehg qimport 'http://people.mozilla.org/~sfink/slowcalls-proto/slowcalls-logger'

That first patch is likely to rot rather quickly. If so, you could clone revision 19b462ec16a0 and copy out the js/src subtree from there instead.

Option 2: tracemonkey

The patches in bug 602067 will get to the same state as the patched mozilla-central tree, above, but dvander has rewritten the JS engine integration in bug 603044 to be much, much nicer. None of my patches will be needed after this lands. But I haven't tried it yet.

Building with instrumentation

You will need to configure with both --enable-functiontimer and --enable-trace-jscalls:

 ac_add_options --enable-trace-jscalls
 ac_add_options --enable-functiontimer

I've also been running with --enable-debug, which probably provides a lot more verbosity in the functiontimer logs. But I haven't tried without it, so I'm not sure.

 ac_add_options --enable-debug

Configure your profile

With the patched mozilla-central variant, the instrumentation will not work with Jaegermonkey, so you'll need to go to about:config and turn off JM:

 javascript.options.methodjit.chrome = false
 javascript.options.methodjit.content = false

If you are using a version that has bug 603044 patch within it, then this will not be an issue (his patch fixes the instrumentation for JM as well.)

Run your scenario

Set the following environment variables before running your scenario:

 NSPR_LOG_MODULES=JSDiagnostics:5
 NSPR_LOG_FILE=/tmp/minefield.log
 MOZ_FT=/tmp/minefield.tl

For example, I run with this command:

 NSPR_LOG_MODULES=JSDiagnostics:5 NSPR_LOG_FILE=/tmp/minefield.log MOZ_FT=/tmp/minefield.tl dist/bin/firefox -no-remote -P Blank

Exit the browser when done.

Produce the jscalls output

Run the 'process-jscall-logs' script from bug 558200 giving the two log files generated above as options, and the '-f slowcalls' flag:

 process-jscall-logs -f slowcalls /tmp/minefield.log /tmp/minefield.tl

(though if you're using the default names, you don't actually have to give them on the command line.) This will produce a file /tmp/slowcalls.html. Go to file:///tmp/slowcalls.html in a browser to view the output.