Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751106AbWBMOqE (ORCPT ); Mon, 13 Feb 2006 09:46:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751278AbWBMOqE (ORCPT ); Mon, 13 Feb 2006 09:46:04 -0500 Received: from mx2.mail.elte.hu ([157.181.151.9]:5010 "EHLO mx2.mail.elte.hu") by vger.kernel.org with ESMTP id S1751106AbWBMOqD (ORCPT ); Mon, 13 Feb 2006 09:46:03 -0500 Date: Mon, 13 Feb 2006 15:44:03 +0100 From: Ingo Molnar To: Roman Zippel Cc: Thomas Gleixner , Andrew Morton , linux-kernel@vger.kernel.org, John Stultz Subject: Re: [PATCH 01/13] hrtimer: round up relative start time Message-ID: <20060213144403.GA21317@elte.hu> References: <1139827927.4932.17.camel@localhost.localdomain> <20060213130143.GA10771@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: -2.2 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-2.2 required=5.9 tests=ALL_TRUSTED,AWL autolearn=no SpamAssassin version=3.0.3 -2.8 ALL_TRUSTED Did not pass through any untrusted hosts 0.6 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2100 Lines: 49 * Roman Zippel wrote: > Hi, > > On Mon, 13 Feb 2006, Ingo Molnar wrote: > > > but there is no 'old behavior' to restore to. The +1 to itimer intervals > > caused artifacts that were hitting users and caused 2.4 -> 2.6 itimer > > regressions, which hrtimers fixed. E.g.: > > > > http://bugzilla.kernel.org/show_bug.cgi?id=3289 > > Ingo, please read correctly, this is mainly about interval timers, > which my patch doesn't change. My patch only fixes the initial start > time. Yeah, i know it's about the start time - what else could it possibly be about? As i wrote: > > so i dont think restoring the first timeout of an interval timer to > > be increased by resolution [which your patch does] has any meaning. > > It 'restores' to half of what 2.6 did prior hrtimers. Doing that > > would be inconsistent and would push the 'sum-up' errors observed > > for interval timers above to be again observable in user-space (if > > user-space does a series of timeouts). What's the point? Your change changes the initial start time to be longer by +1 jiffy. My "restores to half of what 2.6 did" observation was in reference to the start time. The other half is the interval time between timeouts. If you add a +1 jiffy to the start time, you ought to do it for the interval time too. Or do it for neither - which is what we chose to do. Yes, the 2.6 regression in the bugzilla was _mainly_ about the intervals adding a comulative +1, but obviously the behavior should be symmetric: if we use our higher resolution for intervals, we should use it for the start time too. In other words: your patch re-introduces half of the bug on low-res platforms. Users doing a series of one-shot itimer calls would be exposed to the same kind of (incorrect and unnecessary) summing-up errors. What's the point? 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/