Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor

[Supriya Kannery <supriyak@in.ibm.com>]

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.