From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39288) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZK1I3-0000co-Q4 for qemu-devel@nongnu.org; Tue, 28 Jul 2015 05:35:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZK1Hz-0003ZY-PN for qemu-devel@nongnu.org; Tue, 28 Jul 2015 05:35:15 -0400 Received: from mail-ig0-x236.google.com ([2607:f8b0:4001:c05::236]:36493) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZK1Hz-0003YO-Jz for qemu-devel@nongnu.org; Tue, 28 Jul 2015 05:35:11 -0400 Received: by igbij6 with SMTP id ij6so108067304igb.1 for ; Tue, 28 Jul 2015 02:35:11 -0700 (PDT) Date: Tue, 28 Jul 2015 17:35:02 +0800 From: Liu Yuan Message-ID: <20150728093502.GA8357@ubuntu-trusty> References: <1437151464-5458-1-git-send-email-mitake.hitoshi@lab.ntt.co.jp> <20150728085008.GA4291@ubuntu-trusty> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150728085008.GA4291@ubuntu-trusty> Subject: Re: [Qemu-devel] [sheepdog] [PATCH] sheepdog: serialize requests to overwrapping area List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Hitoshi Mitake Cc: Kevin Wolf , sheepdog@lists.wpkg.org, MORITA Kazutaka , Jeff Cody , qemu-devel@nongnu.org, Stefan Hajnoczi , Teruaki Ishizaki On Tue, Jul 28, 2015 at 04:50:08PM +0800, Liu Yuan wrote: > On Sat, Jul 18, 2015 at 01:44:24AM +0900, Hitoshi Mitake wrote: > > Current sheepdog driver only serializes create requests in oid > > unit. This mechanism isn't enough for handling requests to > > overwrapping area spanning multiple oids, so it can result bugs like > > below: > > https://bugs.launchpad.net/sheepdog-project/+bug/1456421 > > I'm a bit late to review the patch since I'm not on the cc list, but I'd like to > get the idea how the mentioned bug relates to the serialization of requests? > > The mentioned bug looks to me more a bug of sheepdog because the create and > write request will only unref a single oid. The bug report is unclear about > why the object idx in inode becomes zero, at least not pointing that it relates > to QEMU. > > But this patch assume QEMU send the requests the wrong way and just vaguely > says it is just wrong without reason. > > What is overrapping requests? As far as I understand, the request that stride > over two objects will be split into two, to make sure all the requests fit the > sheepdog object size. Allow requests run concurrently on different SD objects is > way achieving high performance. This patch mutes this feature, to me, without a > decent reason. > > Probably I miss something hidden, but I'd like someone enlighten me about it > because this patch might slow down QEMU VM over sheepdog. > > Thanks, > Yuan Cc Jeff