From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965549AbXCLLNf (ORCPT ); Mon, 12 Mar 2007 07:13:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965589AbXCLLNe (ORCPT ); Mon, 12 Mar 2007 07:13:34 -0400 Received: from mail.suse.de ([195.135.220.2]:57300 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965587AbXCLLNd (ORCPT ); Mon, 12 Mar 2007 07:13:33 -0400 Date: Mon, 12 Mar 2007 12:13:31 +0100 From: Nick Piggin To: Ingo Molnar Cc: Roland McGrath , akpm@linux-foundation.org, mm-commits@vger.kernel.org, drepper@redhat.com, oleg@tv-sign.ru, sebastien.dugue@bull.net, linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [patch] change futex_wait() to hrtimers Message-ID: <20070312111331.GF28546@wotan.suse.de> References: <200703110814.l2B8EaI1007615@shell0.pdx.osdl.net> <20070312011259.3834A1801C4@magilla.sf.frob.com> <20070312091006.GF21024@elte.hu> <20070312091628.GE28546@wotan.suse.de> <20070312110204.GD2231@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070312110204.GD2231@elte.hu> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 12, 2007 at 12:02:04PM +0100, Ingo Molnar wrote: > > * Nick Piggin wrote: > > > > i dont think we should try to do this. We should not and cannot do > > > anything about all of the artifacts that comes with the use of > > > relative timeouts and schedule_timeout(). > > > > > > basically, using jiffies here (which schedule_timeout() does) is > > > /fundamentally/ imprecise. If you get many interrupts, rounding > > > errors sum up - and there's nothing we can do about it! > > > > Well I did convert futex_wait to an absolute timeout based version in > > the subsequent incremental patch. I think that is OK? > > it still has the rounding artifacts: using timer_list there is no way to > do a precise long sleep based on many small sleeps. OK but that is nothing to do with my patch, but the original futex_wait implementation. > even if this means more work for you (i'm sorry about that!) i'm quite > sure we should take Sebastien's hrtimers based implementation of > futex_wait(), and use the nanosleep method to restart it. There's no > point in further tweaking the imprecise approach: whenever some timeout > needs to be restarted, it's a candidate for hrtimers. Absolute timeout is needed, sure. But once that is done, hrtimers does not fix a bug, does it? > > until then, glibc already handles timeouts and restarts it manually. It isn't timeout handling that is buggy, but EINTR behaviour. And glibc does not handle that here.