Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760152AbXFVWQq (ORCPT ); Fri, 22 Jun 2007 18:16:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755223AbXFVWQj (ORCPT ); Fri, 22 Jun 2007 18:16:39 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:35189 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753741AbXFVWQi (ORCPT ); Fri, 22 Jun 2007 18:16:38 -0400 Date: Sat, 23 Jun 2007 00:15:29 +0200 From: Ingo Molnar To: Daniel Walker Cc: Linus Torvalds , Steven Rostedt , LKML , Andrew Morton , Thomas Gleixner , Christoph Hellwig , john stultz , Oleg Nesterov , "Paul E. McKenney" , Dipankar Sarma , "David S. Miller" , matthew.wilcox@hp.com, kuznet@ms2.inr.ac.ru Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues Message-ID: <20070622221529.GA27445@elte.hu> References: <20070622040014.234651401@goodmis.org> <20070622204058.GA11777@elte.hu> <1182549202.3228.78.camel@dhcp193.mvista.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1182549202.3228.78.camel@dhcp193.mvista.com> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean 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=3.0.3 -2.0 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1366 Lines: 29 * Daniel Walker wrote: > > - tasklets have certain fairness limitations. (they are executed in > > softirq context and thus preempt everything, even if there is > > some potentially more important, high-priority task waiting to be > > executed.) > > Since -rt has been executing tasklets in process context for a long > time, I'm not sure this change would cause to many regressions. > However, it seems like implicit dependencies on "tasklets preempt > everything" might crop up. The other issue is if they don't "preempt > everything" (most of the time), what default priority do we give them > (all of the time)? [...] there is no such guarantee at all (of 'instant preemption'), even with current, softirq-based tasklets. A tasklet might be 'stolen' by another CPU. It might be delayed to the next timer tick (or other softirq execution). Or it might be delayed into a ksoftirqd context, which currently runs at nice +19. So your worry of implicit execution dependencies is unfounded, because, if they existed, they would be bad (and triggerable) bugs today too. 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/