From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759298Ab1FWLlf (ORCPT ); Thu, 23 Jun 2011 07:41:35 -0400 Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:33333 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759254Ab1FWLle (ORCPT ); Thu, 23 Jun 2011 07:41:34 -0400 Message-ID: <4E03266C.50408@kernel.dk> Date: Thu, 23 Jun 2011 13:41:32 +0200 From: Jens Axboe MIME-Version: 1.0 To: Thomas Gleixner CC: Christoph Hellwig , LKML , Peter Zijlstra , Tejun Heo , Ingo Molnar , Linus Torvalds Subject: Re: [patch 1/4] sched: Separate the scheduler entry for preemption References: <20110622174659.496793734@linutronix.de> <20110622174918.813258321@linutronix.de> <20110622184328.GA6475@infradead.org> <4E0245A1.3090903@kernel.dk> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2011-06-22 22:15, Thomas Gleixner wrote: > On Wed, 22 Jun 2011, Jens Axboe wrote: > >> On 2011-06-22 20:43, Christoph Hellwig wrote: >>> On Wed, Jun 22, 2011 at 05:52:13PM -0000, Thomas Gleixner wrote: >>>> Block-IO and workqueues call into notifier functions from the >>>> scheduler core code with interrupts and preemption disabled. These >>>> calls should be made before entering the scheduler core. >>>> >>>> To simplify this, separate the scheduler core code into >>>> __schedule(). __schedule() is directly called from the places which >>>> set PREEMPT_ACTIVE and from schedule(). This allows us to add the work >>>> checks into schedule(), so they are only called when a task voluntary >>>> goes to sleep. >>> >>> I don't think that works. We'll need to flush the block requests even >>> for an involuntary schedule. >> >> Yep, doing it just for voluntary schedule() is pointless, since the >> caller should just do the flushing on his own. The whole point of the >> sched hook was to ensure that involuntary schedules flushed it. > > I guess we talk about different things here. The involuntary is when Seems to be the trend for this patchset, why stop now? :-) > you are preempted, which keeps state unchanged and the current code > already excludes that case. > > If you block on a mutex, semaphore, completion or whatever that's a > different thing. That code calls schedule() not __schedule() and that > will flush your stuff as it does now. OK, thanks for the clarification. You are right, the original kernel did not flush on eg preempt and that wasn't the intent either. The intent was to flush on block only. So behaviour remains identical. -- Jens Axboe