From: Christoph Hellwig <hch@lst.de>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: Kevin Wolf <kwolf@redhat.com>,
Supriya Kannery <supriyak@linux.vnet.ibm.com>,
Prerna Saxena <prerna@linux.vnet.ibm.com>,
Christoph Hellwig <hch@lst.de>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor
Date: Tue, 17 May 2011 17:41:26 +0200 [thread overview]
Message-ID: <20110517154126.GA27700@lst.de> (raw)
In-Reply-To: <4DD192BD.3030200@codemonkey.ws>
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.
next prev parent reply other threads:[~2011-05-17 15:41 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-16 18:10 [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor Supriya Kannery
2011-05-16 18:10 ` [Qemu-devel] [RFC Patch 1/3]Qemu: Enhance "info block" to display cache setting Supriya Kannery
2011-05-17 8:39 ` Kevin Wolf
2011-05-17 9:00 ` supriya kannery
2011-05-16 18:10 ` [Qemu-devel] [RFC Patch 2/3]Qemu: New error classes for file reopen and device insertion Supriya Kannery
2011-05-16 18:11 ` [Qemu-devel] [RFC Patch 3/3]Qemu: Add command "cache_set" for dynamic cache change Supriya Kannery
2011-05-16 20:23 ` [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor Christoph Hellwig
2011-05-16 21:10 ` Anthony Liguori
2011-05-17 9:27 ` supriya kannery
2011-05-17 15:41 ` Christoph Hellwig [this message]
2011-05-20 5:41 ` Supriya Kannery
2011-05-17 9:18 ` supriya kannery
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