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Re: [Xen-devel] [PATCH] [IOEMU]: fix the crash of HVM live migration wit

To: "Zhai, Edwin" <edwin.zhai@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] [IOEMU]: fix the crash of HVM live migration with intensive disk access
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Wed, 12 Aug 2009 12:28:09 +0100
Cc: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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On Wed, 12 Aug 2009, Zhai, Edwin wrote:
> One interface should be better. But I'm not sure about the perf 
> implications. You know, qemu use logdirty for its device emulation even 
> without live migration, e.g. vga screen refresh. Changing to 
> xc_hvm_modified_memory would cause many hypercall to set/get the bitmap 
> in xen...

For vga screen refresh qemu calls xc_hvm_track_dirty_vram and
then cpu_physical_memory_set_dirty; the latter needs only to call
xc_hvm_modified_memory in case logdirty is active.
In facts your patch is modifying logdirty_bitmap only when
logdirty_bitmap != NULL that is when a logdirty event is triggered on

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