From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 2650C6B00EE for ; Sat, 30 Jul 2011 14:33:03 -0400 (EDT) Received: from mail-ww0-f45.google.com (mail-ww0-f45.google.com [74.125.82.45]) (authenticated bits=0) by smtp1.linux-foundation.org (8.14.2/8.13.5/Debian-3ubuntu1.1) with ESMTP id p6UIWU7S002942 (version=TLSv1/SSLv3 cipher=RC4-SHA bits=128 verify=FAIL) for ; Sat, 30 Jul 2011 11:32:31 -0700 Received: by wwj40 with SMTP id 40so3781733wwj.26 for ; Sat, 30 Jul 2011 11:32:30 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: From: Linus Torvalds Date: Sat, 30 Jul 2011 08:32:10 -1000 Message-ID: Subject: Re: [GIT PULL] Lockless SLUB slowpaths for v3.1-rc1 Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Pekka Enberg Cc: cl@linux-foundation.org, akpm@linux-foundation.org, rientjes@google.com, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org 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: - *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 crossing cachelines with a locked op is dubious at best), so there may actually be correctness issues involved too, but it would be interesting to hear if anybody actually just tried it. Hmm? Linus -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org