Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932537AbZJGPUU (ORCPT ); Wed, 7 Oct 2009 11:20:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759352AbZJGPUT (ORCPT ); Wed, 7 Oct 2009 11:20:19 -0400 Received: from tomts22.bellnexxia.net ([209.226.175.184]:41195 "EHLO tomts22-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759332AbZJGPUS (ORCPT ); Wed, 7 Oct 2009 11:20:18 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AlMFAFhJzEpMROOX/2dsb2JhbACBUtVHgjSBdgQ Date: Wed, 7 Oct 2009 11:19:40 -0400 From: Mathieu Desnoyers To: Christoph Lameter Cc: Peter Zijlstra , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, Pekka Enberg , Tejun Heo , Mel Gorman , mingo@elte.hu Subject: Re: [this_cpu_xx V5 19/19] SLUB: Experimental new fastpath w/o interrupt disable Message-ID: <20091007151940.GA10052@Krystal> References: <20091006233654.815079668@gentwo.org> <20091006233733.153341605@gentwo.org> <20091007025440.GB4664@Krystal> <1254906707.26976.225.camel@twins> <20091007124628.GB27363@Krystal> <20091007150257.GA8508@Krystal> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.27.31-grsec (i686) X-Uptime: 11:16:49 up 50 days, 2:06, 3 users, load average: 0.24, 0.27, 0.25 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1418 Lines: 37 * Christoph Lameter (cl@linux-foundation.org) wrote: > On Wed, 7 Oct 2009, Mathieu Desnoyers wrote: > > > Usually, when preemption is disabled, the scheduler restrain from > > executing. *Now the important point*: the criterion that bounds the > > maximum amount of time before the scheduler will re-check for pending > > preemption is when preempt_enable() will re-activate preemption. > > Which creates additional overhead in the allocator. > Which we like to keep as low as possible, I agree. > > But because you run preempt_enable with interrupts off, the scheduler > > check is not done. And it's not done when interrupts are re-activated > > neither. > > Ok so we should be moving the preempt_enable after the irq enable. Then we > will call into the scheduler at the end of the slow path. This may add > significantly more overhead that we had before when we simply disabled > and enabled interrupts... > You are already calling the scheduler when ending the _fast_ path. I don't see the problem with calling it when you end the slow path execution. Mathieu -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- 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/