From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756117AbZAXHtq (ORCPT ); Sat, 24 Jan 2009 02:49:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750961AbZAXHtf (ORCPT ); Sat, 24 Jan 2009 02:49:35 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:49977 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750878AbZAXHte (ORCPT ); Sat, 24 Jan 2009 02:49:34 -0500 Date: Fri, 23 Jan 2009 23:49:12 -0800 From: Andrew Morton To: Jan Kara Cc: linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 01/11] quota: Improve locking Message-Id: <20090123234912.f78d75a0.akpm@linux-foundation.org> In-Reply-To: <1232129299-22018-2-git-send-email-jack@suse.cz> References: <1232129299-22018-1-git-send-email-jack@suse.cz> <1232129299-22018-2-git-send-email-jack@suse.cz> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 16 Jan 2009 19:08:09 +0100 Jan Kara wrote: > static DEFINE_SPINLOCK(dq_list_lock); > +static DEFINE_SPINLOCK(dq_state_lock); > DEFINE_SPINLOCK(dq_data_lock); The chances are very good that two or even three of these locks will all get placed into the same cacheline in main memory. The effects will be quite bad if different CPUs (or, worse, different nodes) are taking these locks. For single, kernel-wide locks like these I think we should almost always pad out to a cacheline. With __cacheline_aligned_in_smp, rather than __cacheline_aligned. Because spinlocks do take space even in uniprocessor builds. There are probably lots of existing locks which should be converted.