From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759174Ab0JYS35 (ORCPT ); Mon, 25 Oct 2010 14:29:57 -0400 Received: from rcsinet10.oracle.com ([148.87.113.121]:43224 "EHLO rcsinet10.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754127Ab0JYS3z (ORCPT >); Mon, 25 Oct 2010 14:29:55 -0400 Date: Mon, 25 Oct 2010 14:26:30 -0400 From: Konrad Rzeszutek Wilk To: Christoph Hellwig , daniel.stodden@citrix.com Cc: Jens Axboe , "Theodore Ts'o" , Jeremy Fitzhardinge , "Xen-devel@lists.xensource.com" , Andreas Dilger , Linux Kernel Mailing List Subject: Re: [Xen-devel] Re: linux-next regression: IO errors in with ext4 and xen-blkfront Message-ID: <20101025182630.GA6036@dumpdata.com> References: <4CBF83A0.8090802@goop.org> <4CBF84C9.6050606@goop.org> <4CC148E5.2030605@kernel.dk> <20101022082916.GA14070@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20101022082916.GA14070@infradead.org> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 22, 2010 at 04:29:16AM -0400, Christoph Hellwig wrote: > In the barriers tree Xen claims to support flushes, but I doesn't. > It never handles REQ_FLUSH requests. Try commenting out the > > blk_queue_flush(info->rq, info->feature_flush); > > call and things should improve. I still need to hear back from Xen > folks how to actually implement a cache flush - they only implement I think we just blindly assume that we would pass the request to the backend. And if the backend is running under an ancient version (2.6.18), the behavior would be quite different. Perhaps we should negotiate with the backend whether it runs under a kernel with the new barrier support? And if so, then enable them? If the backend says it has no idea what we are talking about then disable the barrier support? How does that sound? (Adding Daniel to this email thread as he has much more experience than I do). Daniel, what about the "use tagged queuing for barriers" patch you wrote some time ago? Is it applicable to this issue? > a barrier write privilegue which could never implement an empty > cache flush. Up to current kernels that meant it would implement > barrier writes with content correctly and silently ignore empty barriers > leading to very interesting data integrity bugs. From 2.6.37 onwards > it simply won't work anymore at all, which is at least consistent > (modulo the bug of actually claiming to support flushes). > > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel