From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 30474 invoked by alias); 27 Jan 2012 12:49:45 -0000 Received: (qmail 30459 invoked by uid 22791); 27 Jan 2012 12:49:43 -0000 X-SWARE-Spam-Status: No, hits=-2.9 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00 X-Spam-Check-By: sourceware.org Received: from localhost (HELO gcc.gnu.org) (127.0.0.1) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Fri, 27 Jan 2012 12:49:30 +0000 From: "amacleod at redhat dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug libstdc++/51798] [4.7 regression] libstdc++ atomicity performance regression due to __sync_fetch_and_add Date: Fri, 27 Jan 2012 13:03:00 -0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: libstdc++ X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: amacleod at redhat dot com X-Bugzilla-Status: NEW X-Bugzilla-Priority: P1 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: 4.7.0 X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated Content-Type: text/plain; charset="UTF-8" MIME-Version: 1.0 Mailing-List: contact gcc-bugs-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-bugs-owner@gcc.gnu.org X-SW-Source: 2012-01/txt/msg03133.txt.bz2 http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51798 --- Comment #19 from Andrew Macleod 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?