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Re: [Qemu-devel] [PATCH 7/7] Fake dirty loggin when it's not there

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 7/7] Fake dirty loggin when it's not there
Date: Fri, 17 Jul 2009 14:27:11 +0200

On 17.07.2009, at 14:18, Alexander Graf wrote:

On 17.07.2009, at 14:10, Stefano Stabellini wrote:

On Fri, 17 Jul 2009, Alexander Graf wrote:
Some KVM platforms don't support dirty logging yet, like IA64 and PPC, so in order to still have screen updates on those, we need to fake it.

This patch just tells the getter function for dirty bitmaps, that all pages within a slot are dirty when the slot has dirty logging enabled.

That way we can implement dirty logging on those platforms sometime when
it drags down performance, but share the rest of the code with dirty
logging capable platforms.

Isn't it going to be very very slow?
I think a memcmp based approach as a fallback would be a better idea,
and if we could make this generic it would be even better :)

Oh memcmp not memcpy - sorry I misread that.

Yeah, one could do memcmp there. I don't know if it's worth it though. At least the VNC target does a dirty verification itself again anyways.

Thinking about this again, you'd have to copy it somewhere before. So on every dirty check you'd have to copy all memory off to "somewhere" to be able to check for it again later.

Sounds feasible, but is it really worth the effort? Can Xen do dirty logging?


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