From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752455Ab1GaRkF (ORCPT ); Sun, 31 Jul 2011 13:40:05 -0400 Received: from mga14.intel.com ([143.182.124.37]:65400 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751818Ab1GaRkA (ORCPT ); Sun, 31 Jul 2011 13:40:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.67,296,1309762800"; d="scan'208";a="2800550" From: Andi Kleen To: Linus Torvalds Cc: Pekka Enberg , cl@linux-foundation.org, akpm@linux-foundation.org, rientjes@google.com, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, kosaki.motohiro@jp.fujitsu.com, yinghan@google.com Subject: Re: [GIT PULL] Lockless SLUB slowpaths for v3.1-rc1 References: Date: Sun, 31 Jul 2011 10:39:58 -0700 In-Reply-To: (Linus Torvalds's message of "Sat, 30 Jul 2011 08:32:10 -1000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux) 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 Linus Torvalds writes: > On Sat, Jul 30, 2011 at 8:27 AM, Linus Torvalds > wrote: >> >> Do we allocate the page map array sufficiently aligned that we >> actually don't ever have the case of straddling a cacheline? I didn't >> check. > > Oh, and another thing worth checking: did somebody actually check the > timings for: I would like to see a followon patch that moves the mem_cgroup pointer back into struct page. Copying some mem_cgroup people. > > - *just* the alignment change? > > IOW, maybe some of the netperf improvement isn't from the lockless > path, but exactly from 'struct page' always being in a single > cacheline? > > - check performance with cmpxchg16b *without* the alignment. > > Sometimes especially intel is so good at unaligned accesses that > you wouldn't see an issue. Now, locked ops are usually special (and As Eric pointed out CMPXCHG16B requires alignment, it #GPs otherwise. -Andi -- ak@linux.intel.com -- Speaking for myself only