From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with ESMTP id 4B7DD6B0093 for ; Thu, 18 Mar 2010 20:29:50 -0400 (EDT) Date: Thu, 18 Mar 2010 17:25:58 -0700 From: Greg KH Subject: Re: [RFC PATCH] Fix Readahead stalling by plugged device queues Message-ID: <20100319002558.GD5454@kroah.com> References: <4B979104.6010907@linux.vnet.ibm.com> <20100310130932.GB18509@localhost> <4B97AD52.7080201@linux.vnet.ibm.com> <20100311014542.GA8134@localhost> <4B98BEB0.6020800@linux.vnet.ibm.com> <20100311132913.GB6692@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100311132913.GB6692@localhost> Sender: owner-linux-mm@kvack.org To: Wu Fengguang Cc: Christian Ehrhardt , Jens Axboe , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Martin Schwidefsky , Heiko Carstens , Hisashi Hifumi , KOSAKI Motohiro , Ronald , Bart Van Assche , Vladislav Bolkhovitin , Randy Dunlap , Nick Piggin , Andrew Morton , Greg Kroah-Hartman List-ID: On Thu, Mar 11, 2010 at 09:29:13PM +0800, Wu Fengguang wrote: > On Thu, Mar 11, 2010 at 05:58:08PM +0800, Christian Ehrhardt wrote: > > Wu Fengguang wrote: > > > On Wed, Mar 10, 2010 at 10:31:46PM +0800, Christian Ehrhardt wrote: > > >> > > >> Wu Fengguang wrote: > > >> [...] > > >>> Christian, did you notice this commit for 2.6.33? > > >>> > > >>> commit 65a80b4c61f5b5f6eb0f5669c8fb120893bfb388 > > >> [...] > > >> > > >> I didn't see that particular one, due to the fact that whatever the > > >> result is it needs to work .32 > > >> > > >> Anyway I'll test it tomorrow and if that already accepted one fixes my > > >> issue as well I'll recommend distros older than 2.6.33 picking that one > > >> up in their on top patches. > > > > > > OK, thanks! > > > > That patch fixes my issue completely and is as we discussed less > > aggressive which is fine - thanks for pointing it out - Now I have > > something already upstream accepted to fix the issue, thats much better! > > That's great news, it works beyond my expectation.. :) > > > >>> It should at least improve performance between .32 and .33, because > > >>> once two readahead requests are merged into one single IO request, > > >>> the PageUptodate() will be true at next readahead, and hence > > >>> blk_run_backing_dev() get called to break out of the suboptimal > > >>> situation. > > >> As you saw from my blktrace thats already the case without that patch. > > >> Once the second readahead comes in and merged it gets unplugged in > > >> 2.6.32 too - but still that is bad behavior as it denies my things like > > >> 68% throughput improvement :-). > > > > > > I mean, when readahead windows A and B are submitted in one IO -- > > > let's call it AB -- commit 65a80b4c61 will explicitly unplug on doing > > > readahead C. While in your trace, the unplug appears on AB. > > > > > > The 68% improvement is very impressive. Wondering if commit 65a80b4c61 > > > (the _conditional_ unplug) can achieve the same level of improvement :) > > > > Yep it can ! > > We can post update the patch description to bigger numbers :-) > > Andrew/Greg, shall we push the patch to .32 stable? I've now queued it up. thanks, greg k-h -- 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/ . Don't email: email@kvack.org