From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760332AbXGRVil (ORCPT ); Wed, 18 Jul 2007 17:38:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758286AbXGRVic (ORCPT ); Wed, 18 Jul 2007 17:38:32 -0400 Received: from mail.tmr.com ([64.65.253.246]:38017 "EHLO posidon.tmr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757096AbXGRVib (ORCPT ); Wed, 18 Jul 2007 17:38:31 -0400 Message-ID: <469E8821.3070700@tmr.com> Date: Wed, 18 Jul 2007 17:37:37 -0400 From: Bill Davidsen Reply-To: davidsen@posidon.tmr.com Organization: TMR Associates, Inc User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.4) Gecko/20070509 SeaMonkey/1.1.2 MIME-Version: 1.0 To: Linus Torvalds CC: Ingo Molnar , Ian Kent , Chuck Ebbert , linux-kernel@vger.kernel.org Subject: Re: [patch] CFS scheduler, -v19 References: <20070706173319.GA2356@elte.hu> <1184054902.12336.19.camel@Homer.simpson.net> <469512C1.6090406@tmr.com> <20070711205556.GA27266@elte.hu> <4697EC49.4070303@tmr.com> <469BE462.9030004@redhat.com> <20070716215541.GA27171@elte.hu> <1184648474.3188.33.camel@raven.themaw.net> <20070717074537.GA13539@elte.hu> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds wrote: > On Tue, 17 Jul 2007, Ingo Molnar wrote: > >> * Ian Kent wrote: >> >>> In several places I have code similar to: >>> >>> wait.tv_sec = time(NULL) + 1; >>> wait.tv_nsec = 0; >>> > > Ok, that definitely should work. > > Does the patch below help? > > Spectacularly no! With this patch the "glitch1" script with multiple scrolling windows has all xterms and glxgears stop totally dead for ~200ms once per second. I didn't properly test anything else after that. Since the automount issue doesn't seem to start until something kicks it off, I didn't see it but that doesn't mean it's fixed. >> ah! It passes in a low-res time source into a high-res time interface >> (pthread_cond_timedwait()). Could you change the time(NULL) + 1 to >> time(NULL) + 2, or change it to: >> >> gettimeofday(&wait, NULL); >> wait.tv_sec++; >> > > This is wrong. It's wrong for two reasons: > > - it really shouldn't be needed. I don't think "time()" has to be > *exactly* in sync, but I don't think it can be off by a third of a > second or whatever (as the "30% CPU load" would seem to imply) > > - gettimeofday works on a timeval, pthread_cond_timedwait() works on a > timespec. > > So if it actually makes a difference, it makes a difference for the > *wrong* reason: the time is still totally nonsensical in the tv_nsec field > (because it actually got filled in with msecs!), but now the tv_sec field > is in sync, so it hides the bug. > > Anyway, hopefully the patch below might help. But we probably should make > this whole thing a much more generic routine (ie we have our internal > "getnstimeofday()" that still is missing the second-overflow logic, and > that is quite possibly the one that triggers the "30% off" behaviour). > > Hope that info helps. > Ingo, I'd suggest: > - ger rid of "timespec_add_ns()", or at least make it return a return > value for when it overflows. > - make all the people who overflow into tv_sec call a "fix_up_seconds()" > thing that does the xtime overflow handling. > > Linus >