From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=50961 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Onsy7-0003dD-7b for qemu-devel@nongnu.org; Tue, 24 Aug 2010 08:51:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1Onsy2-0003ov-UD for qemu-devel@nongnu.org; Tue, 24 Aug 2010 08:51:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:26207) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1Onsy2-0003oi-OH for qemu-devel@nongnu.org; Tue, 24 Aug 2010 08:51:06 -0400 From: Juan Quintela In-Reply-To: <1282646430-5777-1-git-send-email-kwolf@redhat.com> (Kevin Wolf's message of "Tue, 24 Aug 2010 12:40:30 +0200") References: <1282646430-5777-1-git-send-email-kwolf@redhat.com> Date: Tue, 24 Aug 2010 14:48:42 +0200 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Subject: [Qemu-devel] Re: [RFC][STABLE 0.13] Revert "qcow2: Use bdrv_(p)write_sync for metadata writes" List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: stefanha@gmail.com, hch@lst.de, mjt@tls.msk.ru, qemu-devel@nongnu.org, avi@redhat.com Kevin Wolf wrote: > This reverts commit 8b3b720620a1137a1b794fc3ed64734236f94e06. > > This fix has caused severe slowdowns on recent kernels that actually do flush > when they are told so. Reverting this patch hurts correctness and means that we > could get corrupted images in case of a host crash. This means that qcow2 might > not be an option for some people without this fix. On the other hand, I get > reports that the slowdown is so massive that not reverting it would mean that > people can't use it either because it just takes ages to complete stuff. It > probably can be fixed, but not in time for 0.13.0. > > Usually, if there's a possible tradeoff between correctness and performance, I > tend to choose correctness, but I'm not so sure in this case. I'm not sure with > reverting either, which is why I post this as an RFC only. > > I hope to get some more comments on how to proceed here for 0.13. I think that we have to revert also. It is a thoug decission so. This patch makes things more "correct", but it makes some load really slow, for instance, and install went from 15m to 50m on my hardware :( My point here is that with the patch, qcow2 becomes almost unusable, so ... what to do? Later, Juan.