This is an archived page. It's not actively maintained.

Profiling SpiderMonkey

Instructions

1.) Get yourself an optimized libxul build of Firefox, with debugger info.

For the Mac, you'll want to read up on Profiling JavaScript with Shark. Here's a sample mozconfig:

mk_add_options MOZ_OBJDIR=@TOPSRCDIR@/ff-opt-libxul
mk_add_options MOZ_MAKE_FLAGS=-j3
ac_add_options --enable-optimize
ac_add_options --enable-libxul
ac_add_options --enable-shark
ac_add_options --enable-debugger-info-modules
ac_add_options --enable-application=browser

2.) You'll want to run Shark on both the browser and [xpcshell], since the host environments differ. Here are some instrumented tests to work from: media:Profiling-ammo.zip

3.) Once you have some changes you'd like to try, you can just rebuild the js/src directory, since it produces its own shared library, even in libxul and static builds.

make -C my-obj-dir/js/src

Other Ways To Profile

For Linux, there are global jprof functions available. See the documentation on the --enable-jprof mozconfig option. We're working to add support for other profilers, such as OProfile, Intel VTune, and Callgrind. When we have JS scriptable profiling options available for all tier 1 platforms, we'll look at adding global start/stop profiling functions.

If you'd like to profile something at a higher level of detail than the JS Shark functions allow, there are corresponding C functions available at the bottom of jsdbgapi.h.

Costs Of Thread Safety

Currently, threadsafe SpiderMonkey costs us 10-15% on some benchmarks vs. a non-threadsafe JS shell. If you're looking to investigate that, build a standalone copy of SpiderMonkey and compare it with xpcshell.