Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750722AbVIDBAy (ORCPT ); Sat, 3 Sep 2005 21:00:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750752AbVIDBAy (ORCPT ); Sat, 3 Sep 2005 21:00:54 -0400 Received: from smtp207.mail.sc5.yahoo.com ([216.136.129.97]:7538 "HELO smtp207.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S1750722AbVIDBAy (ORCPT ); Sat, 3 Sep 2005 21:00:54 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=X/kmRSFq0aLmv9GRc1SUCJwjDc4g2Y6TjwbGCViDZKDRgJSkL9/sZY+e9b/y1IHsDCF6Dc2Wpvtqr35m9VZXvOSf5IdO/sa28GdOQtVFXmOuq0vqiPN5aFBDUU5jBeE00QPo5UDazLv5LQD/b1ENAVlKZnSmvAeM2l9jJXk4YII= ; Message-ID: <431A4767.4030403@yahoo.com.au> Date: Sun, 04 Sep 2005 11:01:27 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.10) Gecko/20050802 Debian/1.7.10-1 X-Accept-Language: en MIME-Version: 1.0 To: Alan Cox CC: Andi Kleen , Linux Memory Management , linux-kernel Subject: Re: [PATCH 2.6.13] lockless pagecache 2/7 References: <4317F071.1070403@yahoo.com.au> <4317F0F9.1080602@yahoo.com.au> <4317F136.4040601@yahoo.com.au> <1125666486.30867.11.camel@localhost.localdomain> <4318C28A.5010000@yahoo.com.au> <1125705471.30867.40.camel@localhost.localdomain> <4318FF2B.6000805@yahoo.com.au> <1125768697.14987.7.camel@localhost.localdomain> In-Reply-To: <1125768697.14987.7.camel@localhost.localdomain> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1313 Lines: 43 Alan Cox wrote: > On Sad, 2005-09-03 at 11:40 +1000, Nick Piggin wrote: > >>We'll see how things go. I'm fairly sure that for my usage it will >>be a win even if it is costly. It is replacing an atomic_inc_return, >>and a read_lock/read_unlock pair. > > > Make sure you bench both AMD and Intel - I'd expect it to be a big loss > on AMD because the AMD stuff will perform atomic locked operations very > efficiently if they are already exclusive on this CPU or a prefetch_w() > on them was done 200+ clocks before. > I will try to get numbers for both. I would be surprised if it was a big loss... but I'm assuming a locked cmpxchg isn't outlandishly expensive. Basically: read_lock_irqsave(cacheline1); atomic_inc_return(cacheline2); read_unlock_irqrestore(cacheline1); Turns into atomic_cmpxchg(); I'll do some microbenchmarks and get back to you. I'm quite interested now ;) What sort of AMDs did you have in mind, Opterons? Thanks, Nick -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com - 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/