From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932544AbYCGCcf (ORCPT ); Thu, 6 Mar 2008 21:32:35 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756294AbYCGCcZ (ORCPT ); Thu, 6 Mar 2008 21:32:25 -0500 Received: from ns.suse.de ([195.135.220.2]:53032 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758841AbYCGCcY (ORCPT ); Thu, 6 Mar 2008 21:32:24 -0500 Date: Fri, 7 Mar 2008 03:32:23 +0100 From: Nick Piggin To: Christoph Lameter Cc: David Miller , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, yanmin_zhang@linux.intel.com, dada1@cosmosbay.com Subject: Re: [rfc][patch 1/3] slub: fix small HWCACHE_ALIGN alignment Message-ID: <20080307023223.GD21185@wotan.suse.de> References: <20080303201701.GF8974@wotan.suse.de> <20080305000637.GA1510@wotan.suse.de> <20080304.161003.129716254.davem@davemloft.net> <20080306025758.GB27150@wotan.suse.de> <20080307022355.GB21185@wotan.suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 06, 2008 at 06:26:49PM -0800, Christoph Lameter wrote: > On Fri, 7 Mar 2008, Nick Piggin wrote: > > > That's just because you (apparently still) have a misconception about what > > the flag is supposed to be for. It is not for aligning things to the start > > of a cacheline boundary. It is not for avoiding false sharing on SMP. It > > The alignment of the object to the start of a cacheline is the obvious > meaning and that is also reflected in the comment in slab.h. It doesn't say start of cache line. It says align them *on* cachelines. 2 32 byte objects on a 64 byte cacheline are aligned on the cacheline. 2.67 24 bytes objects on a 64 byte cacheline are not aligned on the cacheline. Anyway, if you want to be myopic about it, then good luck with that.