From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:36605) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QMGrA-0006ak-7x for qemu-devel@nongnu.org; Tue, 17 May 2011 05:46:25 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1QMGr8-0008Ta-L5 for qemu-devel@nongnu.org; Tue, 17 May 2011 05:46:24 -0400 Received: from e23smtp05.au.ibm.com ([202.81.31.147]:37942) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1QMGr8-0008TI-5D for qemu-devel@nongnu.org; Tue, 17 May 2011 05:46:22 -0400 Received: from d23relay05.au.ibm.com (d23relay05.au.ibm.com [202.81.31.247]) by e23smtp05.au.ibm.com (8.14.4/8.13.1) with ESMTP id p4H9e683029708 for ; Tue, 17 May 2011 19:40:06 +1000 Received: from d23av02.au.ibm.com (d23av02.au.ibm.com [9.190.235.138]) by d23relay05.au.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4H9jhgP1306804 for ; Tue, 17 May 2011 19:45:45 +1000 Received: from d23av02.au.ibm.com (loopback [127.0.0.1]) by d23av02.au.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4H9k4Dl020598 for ; Tue, 17 May 2011 19:46:05 +1000 Message-ID: <4DD23F77.3050407@in.ibm.com> Date: Tue, 17 May 2011 14:57:19 +0530 From: supriya kannery MIME-Version: 1.0 References: <20110516181023.7142.33402.sendpatchset@skannery> <20110516202354.GA8955@lst.de> <4DD192BD.3030200@codemonkey.ws> In-Reply-To: <4DD192BD.3030200@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1; 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: Anthony Liguori Cc: Kevin Wolf , Supriya Kannery , Prerna Saxena , Christoph Hellwig , qemu-devel@nongnu.org Anthony Liguori wrote: > On 05/16/2011 03:23 PM, Christoph Hellwig wrote: >> Why are you even trying this again? As explained very clearly last >> time you >> can't change from a writeback-style to a write-through style I/O from >> the monitor without creating massive data integrity problems. > > 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. > ok > 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). > Will go through the code in detail to understand handling of (1) and (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. > > Regards, > > Anthony Liguori > > See my >> patchset that allows changing this from the guest for how it should be >> done - I just need to get back and revisit the virtio protocol support >> for it. >> >> > >