Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757189AbZJLP1H (ORCPT ); Mon, 12 Oct 2009 11:27:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757169AbZJLP1G (ORCPT ); Mon, 12 Oct 2009 11:27:06 -0400 Received: from tomts5-srv.bellnexxia.net ([209.226.175.25]:55982 "EHLO tomts5-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757105AbZJLP1F (ORCPT ); Mon, 12 Oct 2009 11:27:05 -0400 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AigFAOLn0kpMROOX/2dsb2JhbACBUdVehC0E Date: Mon, 12 Oct 2009 11:26:27 -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: <20091012152627.GA27835@Krystal> References: <1254988350.26976.256.camel@twins> <20091008171750.GA3370@Krystal> <20091008191754.GA12729@Krystal> <20091008203724.GA15798@Krystal> <20091012135600.GB15605@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: 11:25:35 up 55 days, 2:15, 4 users, load average: 0.30, 0.23, 0.21 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: 1572 Lines: 48 * Christoph Lameter (cl@linux-foundation.org) wrote: > On Mon, 12 Oct 2009, Mathieu Desnoyers wrote: > > > > In the middle of the function we have determine that we have to go to the > > > page allocator to get more memory. There is not much the compiler can do > > > to speed that up. > > > > Indeed, the compiler cannot do much about it. However, the programer > > (you) can move the preempt_enable_no_resched() part of the > > preempt_enable() to the beginning of the function. > > Ok but then we have the issue that the later irq enable in the > slowpath will not check for preemption. > > > > > I still recommend the preempt_enable_no_resched() at the beginning of > > > > __slab_alloc(), and simply putting a check_resched() here (which saves > > > > us the odd compiler barrier in the middle of function). > > > > > > Then preemption would be unnecessarily disabled for the page allocator > > > call? > > > > No ? > > preempt_enable_no_resched() enables preemption. > > 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() 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/