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Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change throug
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor |
Date: |
Mon, 16 May 2011 16:10:21 -0500 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110424 Lightning/1.0b2 Thunderbird/3.1.10 |
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.
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.
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.
- [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor, Supriya Kannery, 2011/05/16
- [Qemu-devel] [RFC Patch 1/3]Qemu: Enhance "info block" to display cache setting, Supriya Kannery, 2011/05/16
- [Qemu-devel] [RFC Patch 2/3]Qemu: New error classes for file reopen and device insertion, Supriya Kannery, 2011/05/16
- [Qemu-devel] [RFC Patch 3/3]Qemu: Add command "cache_set" for dynamic cache change, Supriya Kannery, 2011/05/16
- Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor, Christoph Hellwig, 2011/05/16
- Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor,
Anthony Liguori <=
- Re: [Qemu-devel] [RFC Patch 0/3]Qemu: Enable dynamic cache change through qemu monitor, supriya kannery, 2011/05/17