[Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

[Zachary Amsden <zach@xxxxxxxxxx>]

Andi Kleen wrote:
> One thing I was pondering was to replace the expensive popfs with
>
> bt  $IF,(%rsp) 
> jnc 1f 
> sti
> 1: 
>
> But would be mostly a P4 optimization again and I'm not 100% sure it is
> worth it.
>   
Worth it on 32-bit.  On AMD64, probably not.  On Intel 64-bit, maybe, 
but less important than in P4 days.
This could change character completely if used at the tail of a function 
where you now have
sti; 1: ret

Which generates an interrupt holdoff on the ret, an unusual thing to do.

Zach

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