Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752137Ab1EFKXC (ORCPT ); Fri, 6 May 2011 06:23:02 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:59818 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751757Ab1EFKXA (ORCPT ); Fri, 6 May 2011 06:23:00 -0400 Date: Fri, 6 May 2011 12:22:32 +0200 From: Ingo Molnar To: Thomas Gleixner Cc: Andi Kleen , Eric Dumazet , john stultz , lkml , Paul Mackerras , "Paul E. McKenney" , Anton Blanchard Subject: Re: [RFC] time: xtime_lock is held too long Message-ID: <20110506102232.GA11036@elte.hu> References: <1304564090.2943.36.camel@work-vm> <1304574244.32152.666.camel@edumazet-laptop> <1304576495.2943.40.camel@work-vm> <1304604284.3032.78.camel@edumazet-laptop> <1304608095.3032.95.camel@edumazet-laptop> <20110505210118.GI2925@one.firstfloor.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-ELTE-SpamScore: -2.0 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.0 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.3.1 -2.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1238 Lines: 34 * Thomas Gleixner wrote: > On Thu, 5 May 2011, Andi Kleen wrote: > > > > > Another idea would be to prime cache lines to be dirtied in cpu cache > > > > before taking locks, and better pack variables to reduce number of cache > > > > lines. > > > > > > Most variables are packed already in struct timekeeper, which should > > > be pretty cache hot anyway, so I don't know whether we gain much. > > > > There's actually some potential here. I got a moderate speedup in a > > database benchmark with this patch recently. The biggest win > > Numbers please. I'd suggest to create and publish a seqlock usage worst-case testcase, something that runs N threads on an N CPU system. Then precise measurements have to be done on the source of cache misses, the total cost of the timer interrupt, etc. I.e. this should be analyzed and improved properly, not just sloppily slapping a few prefetches here and there, which wont really *solve* anything ... Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/