Re: [Xen-devel] [PATCH 1/3] x86: also allow REP STOS emulation acceleration

[Tim Deegan <tim@xxxxxxx>]

At 15:50 +0000 on 08 Jan (1420728649), Jan Beulich wrote:
> While the REP MOVS acceleration appears to have helped qemu-traditional
> based guests, qemu-upstream (or really the respective video BIOSes)
> doesn't appear to benefit from that. Instead the acceleration added
> here provides a visible performance improvement during very early HVM
> guest boot.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

If I read this right, it's allocating and memset()ing a buffer and
then copying that buffer to the guest?

Would it be better to map the guest frame and write directly?  Edge
cases where the STOS crosses a frame boundary could happen the old way.

Cheers,

Tim.

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