Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761675AbZJNOW0 (ORCPT ); Wed, 14 Oct 2009 10:22:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758461AbZJNOWZ (ORCPT ); Wed, 14 Oct 2009 10:22:25 -0400 Received: from smtp2.ultrahosting.com ([74.213.174.253]:37223 "EHLO smtp.ultrahosting.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756415AbZJNOWY (ORCPT ); Wed, 14 Oct 2009 10:22:24 -0400 Date: Wed, 14 Oct 2009 10:14:25 -0400 (EDT) From: Christoph Lameter X-X-Sender: cl@gentwo.org To: Tejun Heo cc: linux-kernel@vger.kernel.org, Pekka Enberg , Mel Gorman , Mathieu Desnoyers Subject: Re: [this_cpu_xx V6 3/7] Use this_cpu operations in slub In-Reply-To: <4AD53022.2050309@kernel.org> Message-ID: References: <20091007211024.442168959@gentwo.org> <20091007211052.614790286@gentwo.org> <4AD302A8.4010409@kernel.org> <4AD3E23B.8020103@kernel.org> <4AD4950A.6050201@kernel.org> <4AD53022.2050309@kernel.org> 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: 1934 Lines: 47 On Wed, 14 Oct 2009, Tejun Heo wrote: > > __this_cpu_ptr could be converted to this_cpu_ptr but I think the __ are > > useful there too to show that we are in a preempt section. > > That doesn't make much sense. __ for this_cpu_ptr() means "bypass > sanity check, we're knowingly violating the required conditions" not > "we know sanity checks will pass here". Are you defining what __ means for this_cpu_ptr? > > The calls to raw_smp_processor_id and smp_processor_id() are only useful > > in the fallback case. There is no need for those if the arch has a way to > > provide the current percpu offset. So we in effect have two meanings of __ > > right now. > > > > 1. We do not care about the preempt state (thus we call > > raw_smp_processor_id so that the preempt state does not trigger) > > > > 2. We do not need to disable preempt before the operation. > > > > __this_cpu_ptr only implies 1. __this_cpu_add uses 1 and 2. > > Yeah, we need to clean it up. The naming is too confusing. Its consistent if __ means both 1 and 2. If we want to distinguish it then we may want to create raw_this_cpu_xx which means that we do not call smp_processor_id() on fallback but raw_smp_processor_id(). Does not matter if the arch provides a per cpu offset. This would mean duplicating all the macros. The use of raw_this_cpu_xx should be rare so maybe the best approach is to say that __ means only that the macro does not need to disable preempt but it still checks for preemption being off. Then audit the __this_cpu_xx uses and see if there are any that require a raw_ variant. The vm event counters require both no check and no preempt since they can be implemented in a racy way. -- 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/