1329873 - Profiling bug 1269695 with the Gecko Profiler makes us spend ~500ms in ObjectGroup::findAllocationSite

Status: RESOLVED DUPLICATE of bug 1330532

(Core :: JavaScript Engine: JIT, defect)

Description

[(no longer active)]

Attachment: Instruments Profile

STR:

1. Use a clean profile on Nightly and install the Gecko Profiler add-on from https://new.cleopatra.io/
2. Make sure the profiler is running, and the "Show JIT Optimizations" checkbox under the Performance tab of devtools is off.
3. Profile bug 1269695 using Instruments, with Gecko Profiler also running.
4. See the screenshot which is the call to ObjectGroup::findAllocationSite().

Comment 1

[(no longer active)]

Attachment: Instruction view for findAllocationSite

It seems that the loop in is *extremely* hot <http://searchfox.org/mozilla-central/rev/8144fcc62054e278fe5db9666815cc13188c96fa/js/src/vm/ObjectGroup.cpp#1646>

According to sstangl and sfink, this code should only be used to show the JIT information in devtools, so it shouldn't even be running when the Gecko Profiler is on.

Comment 4

[Steve Fink [:sfink] [:s:]]

I'm not sure this is a total dupe. At some point, we'll want to use the JIT inspector information in the profiler itself, so it would be nice to reduce the overhead so that it doesn't completely bias the sampling. I don't know how fundamentally expensive it is, or it can collect all current information in a cheaper way, or if it can be run in a partial information mode. But I think duping this bug is probably fine, if we open up a new bug at the point when we want to pull in the JIT info.