From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KBBZW-00035c-Aj for qemu-devel@nongnu.org; Tue, 24 Jun 2008 12:40:46 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KBBZT-000329-By for qemu-devel@nongnu.org; Tue, 24 Jun 2008 12:40:45 -0400 Received: from [199.232.76.173] (port=59021 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KBBZT-000321-3e for qemu-devel@nongnu.org; Tue, 24 Jun 2008 12:40:43 -0400 Received: from ecfrec.frec.bull.fr ([129.183.4.8]:42864) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KBBZS-0000yh-FU for qemu-devel@nongnu.org; Tue, 24 Jun 2008 12:40:42 -0400 Subject: Re: [Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off From: Laurent Vivier In-Reply-To: <4861156B.30707@suse.de> References: <1213972680.3859.34.camel@frecb07144> <4861156B.30707@suse.de> Content-Type: text/plain; charset=utf-8 Date: Tue, 24 Jun 2008 18:40:34 +0200 Message-Id: <1214325634.3846.6.camel@frecb07144> Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: qemu-devel@nongnu.org Le mardi 24 juin 2008 =C3=A0 17:40 +0200, Kevin Wolf a =C3=A9crit : > Hi Laurent, Hi Kevin, > Laurent Vivier schrieb: > > this patch improves qcow2 I/O performance when used with cache=3Doff. >=20 > Why do you think this patch helps only for cache=3Doff? I have applied > your patch to Xen ioemu (which has no cache=3Doff / O_DIRECT yet) and > I certainly do see a performance gain for large block sizes (using dd). > With small block sizes like 512 bytes or 1k I lose a bit of perfomance, > though. In fact I made some tests with dbench and results were not as good as with cache=3Doff. It's why I spoke only about cache=3Doff. But as said Av= i, dbench is not a good benchmark for this... WITHOUT WITH ide, cache=3Doff,snapshot=3Doff 20.8494 MB/sec 24.0711 MB/sec ide, cache=3Doff,snapshot=3Don 20.9349 MB/sec 24.5031 MB/sec ide, cache=3Don, snapshot=3Doff 23.6612 MB/sec 24.7186 MB/sec ide, cache=3Don, snapshot=3Don 24.1836 MB/sec 24.7678 MB/sec scsi,cache=3Doff,snapshot=3Doff 21.0264 MB/sec 24.6119 MB/sec scsi,cache=3Doff,snapshot=3Don 21.4184 MB/sec 24.6739 MB/sec scsi,cache=3Don, snapshot=3Doff 25.1483 MB/sec 24.8600 MB/sec scsi,cache=3Don, snapshot=3Don 25.2000 MB/sec 25.2758 MB/sec > bonnie++ shows slightly better numbers with this patch, too. In the > case of block reads the improvement is huge and I even got double > throughput. > I also had a look at your code and it seems fine to me. (Except that > the aio callback handlers become even longer, but that is a different > problem...) I modify this patch according Avi comments, and I'll repost it. Thank you for your comments. Regards, Laurent --=20 ------------- Laurent.Vivier@bull.net --------------- "The best way to predict the future is to invent it." - Alan Kay