Re: [Xen-devel] [Patch 2/4] Refining Xsave/Xrestore support

[Haitao Shan <maillists.shan@xxxxxxxxx>]

I don't know but I suppose this won't be a costing instruction at
lease no larger than writing to other CRx registers. But agreed that a
comparison to minimize the cost would be great. I can add that.

Thanks for pointing out.

Shan Haitao

2010/10/27 Jan Beulich <JBeulich@xxxxxxxxxx>:
>>@@ -1367,6 +1384,8 @@ static void __context_switch(void)
>>         memcpy(stack_regs,
>>                &n->arch.guest_context.user_regs,
>>                CTXT_SWITCH_STACK_BYTES);
>>+        if ( cpu_has_xsave )
>>+            set_xcr0(n->arch.xcr0);
>
> How slow is a write to xcr0? I.e. is it worth checking whether
> current xcr0 matches the to be written value?
>
> Jan
>
>

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