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Date: Thu, 07 Oct 2010 07:20:43 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Stephane Eranian <eranian@google.com>
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Subject: Re: [RFC 0/3] Basic support for LWP
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On 10/07/2010 07:11 AM, Stephane Eranian wrote:
> On Thu, Oct 7, 2010 at 3:59 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 10/07/2010 03:46 AM, Stephane Eranian wrote:
>>>
>>> As for the patch itself, I am not an expert at xsave/xrstor, but it seems to
>>> me you could decouple LWP from FPU. I think  Brian had the same comment.
>>> I suspect this can be done and it will certainly look cleaner.
>>>
>>
>> Well, once you're using XSAVE you're not decoupled from the FPU.  Worse,
>> if you're using XSAVE and not honoring CR0.TS you have a major design flaw.
>>
> Is that to say, that if you use LWP you will have to save/restore FPU state even
> though you're not actually using it?
> 

No, but you wouldn't be able to use lazy FPU.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.