From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda1.sgi.com [192.48.157.11]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id p5U1R2pi163729 for ; Wed, 29 Jun 2011 20:27:03 -0500 Received: from ipmail06.adl2.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id E901EE524B9 for ; Wed, 29 Jun 2011 18:27:01 -0700 (PDT) Received: from ipmail06.adl2.internode.on.net (ipmail06.adl2.internode.on.net [150.101.137.129]) by cuda.sgi.com with ESMTP id 8iYE1Y6kGn5p1RWk for ; Wed, 29 Jun 2011 18:27:01 -0700 (PDT) Date: Thu, 30 Jun 2011 11:26:58 +1000 From: Dave Chinner Subject: Re: [PATCH 02/27] xfs: remove the unused ilock_nowait codepath in writepage Message-ID: <20110630012658.GV561@dastard> References: <20110629140109.003209430@bombadil.infradead.org> <20110629140336.717434334@bombadil.infradead.org> <20110630001525.GU561@dastard> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20110630001525.GU561@dastard> 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: Christoph Hellwig Cc: xfs@oss.sgi.com On Thu, Jun 30, 2011 at 10:15:25AM +1000, Dave Chinner wrote: > On Wed, Jun 29, 2011 at 10:01:11AM -0400, Christoph Hellwig wrote: > > wbc->nonblocking is never set, so this whole code has been unreachable > > for a long time. I'm also not sure it would make a lot of sense - > > we'd rather finish our writeout after a short wait for the ilock > > instead of cancelling the whole ioend. > > The problem that the non-blocking code is trying to solve is only > obvious when the disk subsystem is fast enough to drive the flusher > thread to being CPU bound. > > e.g. when you have a disk subsystem doing background writeback > 10GB/s and the flusher thread is put to sleep for 50ms while we wait > for the lock, it can now only push 9.5GB/s. If we just move on, then > we'll spend that 50ms doing useful work on another dirty inode > rather than sleeping onthis one and hence maintaining a 10GB/s > background write rate. > > I'd suggest that the only thing that should be dropped is the > wbc->nonblocking check. Numbers would be good to validate that this > is still relevant, but I don't have a storage subsystem with enough > bandwidth to drive a flusher thread to being CPU bound... I just confirmed that I don't have a fast enough storage system to test this - the flusher thread uses only ~15% of a CPU @ 800MB/s writeback, so I'd need somewhere above 5GB/s of throughput to see any sort of artifact from this change.... Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs