From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id mBENaP2O030393 for ; Sun, 14 Dec 2008 17:36:25 -0600 Date: Mon, 15 Dec 2008 10:36:17 +1100 From: Dave Chinner Subject: Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs] Message-ID: <20081214233617.GD32301@disturbed> References: <493A9BE7.3090001@sandeen.net> <200812131826.25280.Martin@lichtvoll.de> <4943F37B.8080405@sandeen.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4943F37B.8080405@sandeen.net> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Eric Sandeen Cc: linux-xfs@oss.sgi.com, Alan Piszcz , linux-raid@vger.kernel.orgxfs@oss.sgi.com On Sat, Dec 13, 2008 at 11:40:11AM -0600, Eric Sandeen wrote: > Martin Steigerwald wrote: > > > At the moment it appears to me that disabling write cache may often give > > more performance than using barriers. And this doesn't match my > > expectation of write barriers as a feature that enhances performance. > > Why do you have that expectation? I've never seen barriers advertised > as enhancing performance. :) > > I do wonder why barriers on, write cache off is so slow; I'd have > thought the barriers were a no-op. Maybe I'm missing something. Barriers still enforce ordering in this case, so it affects the elevator algorithm.... Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs