From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:49920) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QNIHV-0001s1-FY for qemu-devel@nongnu.org; Fri, 20 May 2011 01:29:50 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QNIHU-0006nb-64 for qemu-devel@nongnu.org; Fri, 20 May 2011 01:29:49 -0400 Received: from e23smtp03.au.ibm.com ([202.81.31.145]:48495) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QNIHT-0006nP-FK for qemu-devel@nongnu.org; Fri, 20 May 2011 01:29:48 -0400 Received: from d23relay04.au.ibm.com (d23relay04.au.ibm.com [202.81.31.246]) by e23smtp03.au.ibm.com (8.14.4/8.13.1) with ESMTP id p4K5Oa68013101 for ; Fri, 20 May 2011 15:24:36 +1000 Received: from d23av04.au.ibm.com (d23av04.au.ibm.com [9.190.235.139]) by d23relay04.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4K5TABq1101936 for ; Fri, 20 May 2011 15:29:15 +1000 Received: from d23av04.au.ibm.com (loopback [127.0.0.1]) by d23av04.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4K5TQP9005202 for ; Fri, 20 May 2011 15:29:27 +1000 Message-ID: <4DD5FF0A.9070100@in.ibm.com> Date: Fri, 20 May 2011 11:11:30 +0530 From: Supriya Kannery MIME-Version: 1.0 References: <20110516181023.7142.33402.sendpatchset@skannery> <20110516202354.GA8955@lst.de> <4DD192BD.3030200@codemonkey.ws> <20110517154126.GA27700@lst.de> In-Reply-To: <20110517154126.GA27700@lst.de> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Christoph Hellwig Cc: Kevin Wolf , qemu-devel@nongnu.org, Prerna Saxena On 05/17/2011 09:11 PM, Christoph Hellwig wrote: > On Mon, May 16, 2011 at 04:10:21PM -0500, Anthony Liguori wrote: >> To further clarify: >> >> Today cache=none|writethrough|writeback does two things. It: >> >> 1) Changes the WCE flag that's visible to the guest >> >> 2) Determines whether the host page cache is used for doing guest I/O >> >> As Christoph is very correct in pointing out, we cannot change (1) at run >> time because this is guest visible. You will break a guest if you do this. >> >> But it's still desirable to be able to change (2) at run time. Before we >> can do this properly though, we need to separate out the logic for setting >> (1) vs. (2). >> >> And ideally, we would allow (1) to be changed by the guest itself at run >> time which allows for full dynamic control. This is what he's referring to >> below. > > Exactly. Setting/clearing the BDRV_O_NO_FLUSH also seems useful, maybe > in addition to also allowing an equivalent for the writethrough modes. > Posted second version of the patchset (RFC) which supports only hostcache setting/clearing from qemu monitor. http://www.mail-archive.com/qemu-devel@nongnu.org/msg64658.html Please comment.