Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757057AbZJLPAH (ORCPT ); Mon, 12 Oct 2009 11:00:07 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756540AbZJLPAG (ORCPT ); Mon, 12 Oct 2009 11:00:06 -0400 Received: from smtp2.ultrahosting.com ([74.213.174.253]:58228 "EHLO smtp.ultrahosting.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756461AbZJLPAF (ORCPT ); Mon, 12 Oct 2009 11:00:05 -0400 Date: Mon, 12 Oct 2009 10:52:29 -0400 (EDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Mathieu Desnoyers 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 In-Reply-To: <20091012135600.GB15605@Krystal> Message-ID: References: <20091007151940.GA10052@Krystal> <1254988350.26976.256.camel@twins> <20091008171750.GA3370@Krystal> <20091008191754.GA12729@Krystal> <20091008203724.GA15798@Krystal> <20091012135600.GB15605@Krystal> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1236 Lines: 31 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. -- 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/