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

["Magenheimer, Dan (HP Labs Fort Collins)" <dan.magenheimer@xxxxxx>]

> >   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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