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[Bug libstdc++/51798] [4.7 regression] libstdc++ atomicity performance regression due to __sync_fetch_and_add
- From: "amacleod at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 27 Jan 2012 12:49:27 +0000
- Subject: [Bug libstdc++/51798] [4.7 regression] libstdc++ atomicity performance regression due to __sync_fetch_and_add
- Auto-submitted: auto-generated
- References: <bug-51798-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798
--- Comment #19 from Andrew Macleod <amacleod at redhat dot com> 2012-01-27 12:49:27 UTC ---
(In reply to comment #17)
> (In reply to comment #13)
> > Any code that explicitly calls __sync_* in
> > libstdc++-v3 has introduced a performance regression.
>
> But if it happens in code that is executed only rarely (e.g. the EH code will
> be dominated by time spent in the unwinder, not any barriers), then it might
> not be even measurable. So I think we should first change atomicity.h and only
> if you can come up with a testcase which shows a significant regression for the
> libsupc++ or parallel bits, we should change those too at this point. We are
> in stage4.
Precisely my thoughts... Its not a regression if it isn't measurable, and we
want to change as little as we possibly can at this stage. The patch is what I
was thinking.
I presume it generates the same code power use to get?