From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752850AbZAZWU6 (ORCPT ); Mon, 26 Jan 2009 17:20:58 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755113AbZAZWUp (ORCPT ); Mon, 26 Jan 2009 17:20:45 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:60536 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752214AbZAZWUo (ORCPT ); Mon, 26 Jan 2009 17:20:44 -0500 Date: Mon, 26 Jan 2009 23:20:02 +0100 From: Ingo Molnar To: Andrew Morton Cc: oleg@redhat.com, a.p.zijlstra@chello.nl, rusty@rustcorp.com.au, travis@sgi.com, mingo@redhat.com, davej@redhat.com, cpufreq@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] work_on_cpu: Use our own workqueue. Message-ID: <20090126222002.GB10215@elte.hu> References: <20090126171618.GA32091@elte.hu> <20090126103529.cb124a58.akpm@linux-foundation.org> <20090126202022.GA8867@elte.hu> <20090126130046.37b8f34e.akpm@linux-foundation.org> <20090126212727.GA13670@elte.hu> <20090126133551.fab5e27a.akpm@linux-foundation.org> <20090126214516.GA22142@elte.hu> <20090126140116.35f9c173.akpm@linux-foundation.org> <20090126220537.GA6755@elte.hu> <20090126141605.707877bb.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090126141605.707877bb.akpm@linux-foundation.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Andrew Morton wrote: > On Mon, 26 Jan 2009 23:05:37 +0100 > Ingo Molnar wrote: > > > > > * Andrew Morton wrote: > > > > > Well it turns out that I was having a less-than-usually-senile moment: > > > > > > : implement flush_work() > > > > > Why isn't that working in this case?? > > > > how would that work in this case? We defer processing into the workqueue > > exactly because we want its per-CPU properties. > > It detaches the work item, moves it to head-of-queue, reinserts it then > waits on it. I think. > > This might have a race+hole. If a currently-running "unrelated" work > item tries to take the lock which the flush_work() caller is holding > then there's no way in which keventd will come back to execute the work > item which we just put on the head of queue. Correct - or the unrelated worklet might also be blocked on something - so the window is rather large. > > We want work_on_cpu() to be done in the workqueue context on the CPUs > > that were specified, not in the local CPU context. > > flush_work() is supposed to work in the way which you describe. > > But Oleg's "we may be running on a different CPU" comment has me all > confused. well, we call this on any arbitrary CPU: long work_on_cpu(unsigned int cpu, long (*fn)(void *), void *arg) To execute fn() on 'cpu'. We converted wacky callers that did direct p->cpus_allowed twiddling (and on-stack saving) and set_cpus_allowed() calls to this elegant-looking work_on_cpu() call which just promised exactly this functionality but cleanly so. Ingo