From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 26 Jul 2002 03:23:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 26 Jul 2002 03:23:00 -0400 Received: from e2.ny.us.ibm.com ([32.97.182.102]:5820 "EHLO e2.ny.us.ibm.com") by vger.kernel.org with ESMTP id ; Fri, 26 Jul 2002 03:22:59 -0400 Date: Fri, 26 Jul 2002 12:56:05 +0530 From: Kiran To: Rusty Russell Cc: linux-kernel@vger.kernel.org, torvalds@transmeta.com Subject: Re: Patch 2.5.25: Ensure xtime_lock and timerlist_lock are on difft cachelines Message-ID: <20020726125605.A2822@phreaker.net> References: <20020725204512.E3594@in.ibm.com> <20020726063124.5114E45D6@lists.samba.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20020726063124.5114E45D6@lists.samba.org>; from rusty@rustcorp.com.au on Fri, Jul 26, 2002 at 04:24:51PM +1000 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 26, 2002 at 04:24:51PM +1000, Rusty Russell wrote: > In message <20020725204512.E3594@in.ibm.com> you write: > > I've noticed that xtime_lock and timerlist_lock ends up on the same > > cacheline all the time (atleaset on x86). Not a good thing for > > loads with high xxx_timer and do_gettimeofday counts I guess (networking etc) > .. > > Better might be to use the x86-64 trick of using sequence counters > around do_gettimeofday, and avoid the xtime lock altogether. That > will improve gettimeofday performance as well. Or you could try > changing xtime lock to a brlock. > Ok, I'll look at the x86-64 code > FYI: as policy, I don't take optimization patches without > measurements. I'm just not that smart. > This patch was not meant to be a definitive fix for do_gettimeofday. I thought having diffrent locks on the same cacheline was bad. Atleast, I don't think there'd be any negative performance impact due to my patch. Pls correct me if I am wrong. I want to get some nos too .. and probably will...(still waiting for my turn to use the 4way here :-) ). But, I decided to post this patch as a follow up to the 2.5 profiler discussion on lse-tech. Anywayz, point taken. Next time I submit an optimization patch to you, I'll post the measuements too. Thanks, Kiran