From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KBAg3-0004ds-Ul for qemu-devel@nongnu.org; Tue, 24 Jun 2008 11:43:27 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KBAg1-0004dg-IT for qemu-devel@nongnu.org; Tue, 24 Jun 2008 11:43:26 -0400 Received: from [199.232.76.173] (port=50028 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KBAg1-0004dd-Ch for qemu-devel@nongnu.org; Tue, 24 Jun 2008 11:43:25 -0400 Received: from ns.suse.de ([195.135.220.2]:40560 helo=mx1.suse.de) by monty-python.gnu.org with esmtps (TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60) (envelope-from ) id 1KBAg0-0006aU-M9 for qemu-devel@nongnu.org; Tue, 24 Jun 2008 11:43:24 -0400 Message-ID: <4861156B.30707@suse.de> Date: Tue, 24 Jun 2008 17:40:27 +0200 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH] qcow2: improve I/O performance with cache=off References: <1213972680.3859.34.camel@frecb07144> In-Reply-To: <1213972680.3859.34.camel@frecb07144> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Laurent Vivier Cc: qemu-devel@nongnu.org Hi Laurent, Laurent Vivier schrieb: > this patch improves qcow2 I/O performance when used with cache=off. Why do you think this patch helps only for cache=off? I have applied your patch to Xen ioemu (which has no cache=off / 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. 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...) Kevin