RE: [Xen-ia64-devel] [PATCH 1/2] [RESEND] FPSWA emulation support

[Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>]

Hi Dan/Alex,

Thanks for your information and advice.
I will correct and resend this patch.
 - I remove handle_fpu_swa_for_xen(). and,
 - When an FP error occurs in Xen, Xen does the panic.

Best regards,
 Kan

>> >   Why do we need handle_fpu_swa_for_xen()?  Xen should 
>> never hit an FP
>> >error that requires this support.  Thanks,
>> 
>> Same as you, I think that Xen should never hit an FP error 
>> that requires 
>> this support. However, the time when FPSWA is necessary for 
>> Xen may come.
>> Therefore I'd like to leave handle_fpu_swa_for_xen().
>
>I have to disagree.  An FP error that requires handling
>by the FPSWA is very rare, even in applications that do
>lots of floating point processing.
>
>Linux/ia64 does no floating point processing, Xen/x86 does
>no floating point processing, and Xen/ia64 shouldn't either.
>If some developer adds floating point code into Xen/x86,
>guests will break.  (This happened once last year --
>someone added floating point code to compute some statistics.)
>
>Linux/ia64 uses floating point registers only for integer
>multiply/divide (and? fast copy?).  The same is true of Xen/ia64.
>If any Xen/ia64 developer adds any floating point code
>in Xen that could possibly cause an FPSWA, I'd rather see
>a panic so that code could be removed or fixed.
>
>Last, it is not Linux or Xen style to add code that might
>possibly be used sometime in the future.  A kernel and a
>hypervisor should be as small as possible and adding
>even a few hundred bytes of code that maybe will be
>executed sometime in the future (or, in my opinion, never
>should be) is bad style.  At best, the code should be
>surrounded by an "#if 0", and I don't think even that
>is a good idea.
>
>Just my opinion... others may disagree.
>Dan


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