1362894 - The cost of PROFILER_LABEL() is way too high

Status: RESOLVED FIXED

(Core :: Gecko Profiler, enhancement)

Description

[(no longer active)]

On a perf profile of bug 944127 on a local build of trunk without the Gecko Profiler add-on installed, 1.57% of the total time is spent under PseudoStack::push() and 0.88% of the total time is spent under profiler_call_enter() and 0.34% of the total time is spent under profiler_call_exit(), and these are both coming from <https://searchfox.org/mozilla-central/rev/8b70b0a5038ef9472fe7c53e04a70c978bb06aed/layout/style/nsStyleSet.cpp#1101>.

Our first option is to remove this PROFILER_LABEL.  But there is a lot we can do to make these more efficient.

Perf says that one performance issue with profile_call_enter is that it's non-inline (same with profile_call_exit and in fact that is the *only* performance problem with it.)  The other issue is the TLS access there.  I'm not sure what we can do about that.  The profile us a lot less conclusive about push() because perf gets confused when annotating it and it shows me an unrelated function mostly.

Comment 1

[(no longer active)]

profiler_call_enter and profiler_call_exit were uninlined in bug 1359000.

Nick, can we revert that decision?

Comment 2

[Nicholas Nethercote [inactive]]

I'll look at this tomorrow.

Comment 3

[Nicholas Nethercote [inactive]]

Attachment: Make profiler_call_{enter,exit} |inline|

Bug 1359000 moved these functions from GeckoProfiler.h to platform.cpp, which
allowed a lot of follow-up simplifications. But it hurt performance.

This patch moves them back to GeckoProfiler.h and makes them |inline| again.
This required adding a second TLS pointer, sPseudoStack. Comments in the patch
explain why.

Comment 4

[Nicholas Nethercote [inactive]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/17c6f55e1bdc5c931f12c9893b76cd77ecf39918
Bug 1362894 - Make profiler_call_{enter,exit} |inline|. r=mstange.

Comment 5

[Carsten Book [:Tomcat]]

https://hg.mozilla.org/mozilla-central/rev/17c6f55e1bdc