Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755539Ab1C3CJu (ORCPT ); Tue, 29 Mar 2011 22:09:50 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:43202 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754148Ab1C3CJt (ORCPT ); Tue, 29 Mar 2011 22:09:49 -0400 Date: Tue, 29 Mar 2011 19:10:07 -0700 From: Andrew Morton To: Shaohua Li Cc: Andi Kleen , linux-mm , lkml , Rik van Riel , Hugh Dickins Subject: Re: [PATCH]mmap: add alignment for some variables Message-Id: <20110329191007.04e8376a.akpm@linux-foundation.org> In-Reply-To: <1301450041.3981.55.camel@sli10-conroe> References: <1301277536.3981.27.camel@sli10-conroe> <1301360054.3981.31.camel@sli10-conroe> <20110329152434.d662706f.akpm@linux-foundation.org> <1301446882.3981.33.camel@sli10-conroe> <20110329180611.a71fe829.akpm@linux-foundation.org> <1301447843.3981.48.camel@sli10-conroe> <20110329182544.6ad4eccb.akpm@linux-foundation.org> <1301449000.3981.52.camel@sli10-conroe> <20110329184110.0086924e.akpm@linux-foundation.org> <1301450041.3981.55.camel@sli10-conroe> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; 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 Content-Length: 1408 Lines: 36 On Wed, 30 Mar 2011 09:54:01 +0800 Shaohua Li wrote: > On Wed, 2011-03-30 at 09:41 +0800, Andrew Morton wrote: > > On Wed, 30 Mar 2011 09:36:40 +0800 Shaohua Li wrote: > > > > > > how is it that this improves things? > > > Hmm, it actually is: > > > struct percpu_counter { > > > spinlock_t lock; > > > s64 count; > > > #ifdef CONFIG_HOTPLUG_CPU > > > struct list_head list; /* All percpu_counters are on a list */ > > > #endif > > > s32 __percpu *counters; > > > } __attribute__((__aligned__(1 << (INTERNODE_CACHE_SHIFT)))) > > > so lock and count are in one cache line. > > > > ____cacheline_aligned_in_smp would achieve that? > ____cacheline_aligned_in_smp can't guarantee the cache alignment for > multiple nodes, because the variable can be updated by multiple > nodes/cpus. Confused. If an object is aligned at a mulitple-of-128 address on one node, it is aligned at a multiple-of-128 address when viewed from other nodes, surely? Even if the cache alignment to which you're referring is the internode cache, can a 34-byte, L1-cache-aligned structure ever span multiple internode cachelines? -- 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/