From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:36651) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qbte6-0000CO-9b for Qemu-devel@nongnu.org; Wed, 29 Jun 2011 08:13:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Qbte4-000170-9C for Qemu-devel@nongnu.org; Wed, 29 Jun 2011 08:13:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15046) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Qbte3-00016o-QZ for Qemu-devel@nongnu.org; Wed, 29 Jun 2011 08:13:28 -0400 Message-ID: <4E0B1787.30709@redhat.com> Date: Wed, 29 Jun 2011 14:16:07 +0200 From: Kevin Wolf MIME-Version: 1.0 References: <4E0B1399.4050807@redhat.com> <4E0B152B.1000201@codemonkey.ws> In-Reply-To: <4E0B152B.1000201@codemonkey.ws> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Default cache mode List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: Avi Kivity , Christoph Hellwig , Qemu-devel@nongnu.org, Stefan Hajnoczi Am 29.06.2011 14:06, schrieb Anthony Liguori: > On 06/29/2011 06:59 AM, Kevin Wolf wrote: >> Hi, >> >> I think we have touched this topic before during some IRC discussions or >> somewhere deep in a mailing list thread, but I think it hasn't been >> discussed on the list. >> >> Our default cache mode of cache=writethrough is extremely conservative >> and provides absolute safety at the cost of performance, > > But for the most part, we track bare metal fairly well in terms of block > performance, no? > > Or are you really referring to qcow2 as a specific example? In the > past, we used a different default caching mode for qcow2. I think that > could be done again if there was a compelling reason. No, people are also complaining about bad performance with raw. Which isn't really surprising when you do a flush after each single write request. O_SYNC is really much more than is needed in the average case. Kevin