From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 3200 invoked by alias); 20 Dec 2012 16:21:18 -0000 Received: (qmail 3191 invoked by uid 22791); 20 Dec 2012 16:21:16 -0000 X-SWARE-Spam-Status: No, hits=-1.9 required=5.0 tests=AWL,BAYES_00,RCVD_IN_DNSWL_NONE,T_RP_MATCHES_RCVD X-Spam-Check-By: sourceware.org Received: from atrey.karlin.mff.cuni.cz (HELO atrey.karlin.mff.cuni.cz) (195.113.26.193) by sourceware.org (qpsmtpd/0.43rc1) with ESMTP; Thu, 20 Dec 2012 16:20:59 +0000 Received: by atrey.karlin.mff.cuni.cz (Postfix, from userid 4018) id 0EED481017; Thu, 20 Dec 2012 17:20:54 +0100 (CET) Date: Thu, 20 Dec 2012 16:21:00 -0000 From: Jan Hubicka To: Rong Xu Cc: Andrew Pinski , GCC Patches , David Li , reply@codereview.appspotmail.com Subject: Re: [google 4.7] atomic update of profile counters (issue6965050) Message-ID: <20121220162054.GA26643@atrey.karlin.mff.cuni.cz> References: <20121219200828.73DB9106927@rong.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) X-IsSubscribed: yes Mailing-List: contact gcc-patches-help@gcc.gnu.org; run by ezmlm Precedence: bulk List-Id: List-Archive: List-Post: List-Help: Sender: gcc-patches-owner@gcc.gnu.org X-SW-Source: 2012-12/txt/msg01254.txt.bz2 > On Wed, Dec 19, 2012 at 4:29 PM, Andrew Pinski wrote: > > > > On Wed, Dec 19, 2012 at 12:08 PM, Rong Xu wrote: > > > Hi, > > > > > > This patch adds the supprot of atomic update the profile counters. > > > Tested with google internal benchmarks and fdo kernel build. > > > > I think you should use the __atomic_ functions instead of __sync_ > > functions as they allow better performance for simple counters as you > > can use __ATOMIC_RELAXED. > > You are right. I think __ATOMIC_RELAXED should be OK here. > Thanks for the suggestion. > > > > > And this would be useful for the trunk also. I was going to implement > > this exact thing this week but some other important stuff came up. > > I'll post trunk patch later. Yes, I like that patch, too. Even if the costs are quite high (and this is why atomic updates was sort of voted down in the past) the alternative of using TLS has problems with too-much per-thread memory. While there are even more alternatives, like recording the changes and commmiting them in blocks (say at function return), I guess some solution is better than no solution. Thanks, Honza