From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1L6w0L-0005E5-Da for qemu-devel@nongnu.org; Sun, 30 Nov 2008 18:47:09 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1L6w0K-0005Dt-KJ for qemu-devel@nongnu.org; Sun, 30 Nov 2008 18:47:08 -0500 Received: from [199.232.76.173] (port=36502 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1L6w0K-0005Dq-Df for qemu-devel@nongnu.org; Sun, 30 Nov 2008 18:47:08 -0500 Received: from hall.aurel32.net ([88.191.82.174]:55710) by monty-python.gnu.org with esmtps (TLS-1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1L6w0K-0003Sd-8g for qemu-devel@nongnu.org; Sun, 30 Nov 2008 18:47:08 -0500 Received: from aurel32 by hall.aurel32.net with local (Exim 4.63) (envelope-from ) id 1L6w0I-0001qA-C1 for qemu-devel@nongnu.org; Mon, 01 Dec 2008 00:47:06 +0100 Date: Mon, 1 Dec 2008 00:47:06 +0100 From: Aurelien Jarno Subject: Re: [Qemu-devel] [5839] qemu-img: open files with cache=writeback Message-ID: <20081130234706.GA29460@hall.aurel32.net> References: <49331A17.2080707@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <49331A17.2080707@codemonkey.ws> Sender: Aurelien Jarno Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org On Sun, Nov 30, 2008 at 04:56:23PM -0600, Anthony Liguori wrote: > Aurelien Jarno wrote: > >Revision: 5839 > > http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=5839 > >Author: aurel32 > >Date: 2008-11-30 19:12:49 +0000 (Sun, 30 Nov 2008) > > > >Log Message: > >----------- > >qemu-img: open files with cache=writeback > > > >Data integrity is not important in qemu-img, so open the files with > >cache=writeback. This fixes the performance regression seen with qemu-img > >since revision 5485, and most particularly with the qcow2 format. > > > >Signed-off-by: Aurelien Jarno > > > > My thinking was to just make qcow2 always default to cache=writeback. I > posted an RFC but received no feedback. I guess that means noone > disagreed :-) > Sorry if I haven't answered to your RFC, but as you said no complains means the patch is ok. I think you can commit it. I have tried your patch to solve the problem, but it was not fixing all the problems: other formats are also affected by the slowdown, as the I/O operations in qemu-img are very different than in qemu. -- .''`. Aurelien Jarno | GPG: 1024D/F1BCDB73 : :' : Debian developer | Electrical Engineer `. `' aurel32@debian.org | aurelien@aurel32.net `- people.debian.org/~aurel32 | www.aurel32.net