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From: | supriya kannery |
Subject: | Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor |
Date: | Tue, 17 May 2011 14:57:19 +0530 |
User-agent: | Thunderbird 2.0.0.14 (X11/20080501) |
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 youcan'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/OAs 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 mypatchset 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.
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