Re: [PATCH] Remove redundant MSR save/restore

Avi Kivity
2007-04-25T09:28:39Z

Dong, Eddie wrote:
> Avi:
> Thanks!
> Another found is that HOST_FS/GS_BASE & MSR_FS/GS_BASE
> save/restore is quit expansive. I am not sure why it needs to be
> save/restored given that the VMCS regster will be loaded into FS/gs at
> VM EXIT time automatically by HW and will not be changed during guest
> execution time. The MSR is also same (guest change will be trap and
> emulated in guest context only).
> If I remove HOST_FS/GS_BASE save/restore out to be only matter
> to userspace, I can get 15% performance gain for KB. But I am not sure
> yet if there is any potential issue.
>
> thanks, eddie
>

I don't see issues with moving them outside the loop, as long as
preemption is disabled.

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