Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932596AbZJLPj1 (ORCPT ); Mon, 12 Oct 2009 11:39:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932574AbZJLPj0 (ORCPT ); Mon, 12 Oct 2009 11:39:26 -0400 Received: from tomts10.bellnexxia.net ([209.226.175.54]:64813 "EHLO tomts10-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932572AbZJLPjY (ORCPT ); Mon, 12 Oct 2009 11:39:24 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AigFABzo0kpMROOX/2dsb2JhbACBUdVfhC0E Date: Mon, 12 Oct 2009 11:38:44 -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: <20091012153844.GA29116@Krystal> References: <20091008171750.GA3370@Krystal> <20091008191754.GA12729@Krystal> <20091008203724.GA15798@Krystal> <20091012135600.GB15605@Krystal> <20091012152627.GA27835@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: 11:36:15 up 55 days, 2:25, 3 users, load average: 0.54, 0.35, 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: 1201 Lines: 54 * Christoph Lameter (cl@linux-foundation.org) wrote: > On Mon, 12 Oct 2009, Mathieu Desnoyers wrote: > > > > If I just enable interrupts there then the preempt check will not be > > > done and we may miss a scheduling point. > > > > > > > That's why you should do: > > > > local_irq_save() > > preempt_enable_no_resched() > > ... > > local_irq_restore() > > preempt_check_resched() > > What is the difference then to > > local_irq_save() > > ... > > local_irq_enable(); > preempt_enable(); > > ? local_irq_save() preempt_enable_no_resched() <- barrier() ... local_irq_enable() preempt_check_resched() vs local_irq_save() ... local_irq_enable(); preempt_enable(); <- barrier() In the first scenario, the compiler barrier is at the beginning of the slow path function, which should impose less restrictions on the compiler optimizations. 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/