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SubjectRe: [PATCH 1/7] KVM: userspace interface
Avi Kivity wrote:
> Anthony Liguori wrote:
>>>
>>> writel(dst_x_reg, x);
>>> writel(dst_y_reg, y)
>>> writel(width_reg, w);
>>> writel(height_reg, h);
>>> writel(blt_cmd_reg, fill);
>>>
>>> then kvm would cache the first four in a mmap()able memory area and
>>> only exit to userspace on the fifth. Userspace would then read the
>>> cached registers from memory and emulate the command.
>>
>> Letting QEMU do a certain amount of emulation after every transition
>> would the problem in a more elegant and generic way.
>>
>
> But what amount? A basic block, or several?
>
> Emulation has its costs. You need to marshal the registers to and
> fro. You need to reset qemu's cached translations. You need to throw
> away shadow page tables and qemu's softmmu. You increase the time
> spent in single threaded code.

Admittedly still a research topic. If you're interested in what we're
doing in Xen, check out:

http://xenbits.xensource.com/ext/xen-unstable-hvm.hg (sorry, xenbits is
down right now but hopefully it will be fixed quickly).

Regards,

Anthony Liguori

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