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Re: [Xen-devel] Test if on newer xen all SSE2 and SSE3 instructions are effectively working

On 21/11/13 15:22, Andrew Cooper wrote:
On 21/11/13 15:12, George Dunlap wrote:
On Thu, Nov 21, 2013 at 10:52 AM, Fabio Fantoni <fabio.fantoni@xxxxxxx> wrote:
I'm trying to test if on newer xen all SSE2 and SSE3 instructions are
effectively working.
I tried this simple program to test SSE2:
But probably use only instructions with short operand because SSE2 on this
program is working also on old xen 4.0 where Jan Beulich patches to support
long operands are missing.
Are there any minimal program to test if SSE instructions with MMIO operands
8 byte are working?
I don't see the code there doing MMIO -- it's just doing operations on
normal RAM, which is not emulated by Xen at all, but executed natively
by the processor.

What you need is a program that will do this to an MMIO region -- that
will be a much trickier thing to set up, I think.

The problem with SSE is only when the guest performs an SSE (or larger)
operation on a piece of memory which ends up being emulated and handed
to qemu.  The ioreq protocol doesn't have a way of signalling an operand
width greater than 64 bits.

I'd like to emphasize the "and" in the first sentence. You might be able to trigger a Xen emulation in any number of ways (disabling HAP and then doing an SSE instruction on an in-use PT might do it). But Xen allegedly already does the actual emulation correctly -- as Andy said, it's only the path to qemu that wasn't working before.


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