From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [Qemu-devel] Re: KVM call minutes for Sept 14 Date: Wed, 15 Sep 2010 08:52:51 -0500 Message-ID: <4C90CFB3.1000708@codemonkey.ws> References: <20100914144758.GA19949@x200.localdomain> <4C8F90A9.8030407@codemonkey.ws> <4C908418.9070301@redhat.com> <4C90BB8E.1020201@codemonkey.ws> <4C90BE28.7060008@redhat.com> <4C90C855.5010306@codemonkey.ws> <4C90CA5A.1040200@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Chris Wright , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Kevin Wolf Return-path: Received: from mail-yx0-f174.google.com ([209.85.213.174]:43157 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753650Ab0IONwz (ORCPT ); Wed, 15 Sep 2010 09:52:55 -0400 Received: by yxp4 with SMTP id 4so68231yxp.19 for ; Wed, 15 Sep 2010 06:52:54 -0700 (PDT) In-Reply-To: <4C90CA5A.1040200@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 09/15/2010 08:30 AM, Kevin Wolf wrote: > Am 15.09.2010 15:21, schrieb Anthony Liguori: > >> On 09/15/2010 07:38 AM, Kevin Wolf wrote: >> >>> No, we don't really care if the L2 entry is on disk. If the guest want >>> to have its data safe it needs to issue an explicit flush anyway. The >>> only thing we want to achieve with bdrv_write_sync is to maintain the >>> right order between metadata updates to survive a crash without corruption. >>> >>> >> Ah, yes, this is brand new :-) >> >> I was looking at my QED branch which is a few weeks old. >> > Well, the whole bdrv_pwrite_sync thing is new - with your benchmarking > you probably caught qcow2 at its worst performance in years. FWIW, we queued a run reverting the sync() stuff entirely as we were aware of that. Should have results this morning. > Initially I > just blindly converted everything to be on the safe side, and now we > need to optimize to get the performance back. There are probably some > more syncs that can be removed in less common paths. > Most likely. Regards, Anthony Liguori > Kevin >