[ECOS] FPU support implementation question.

Jonathan Larmour jlarmour@redhat.co.uk
Tue Apr 11 10:13:00 GMT 2000

Patrick O'Grady wrote:
> - Don't make it configurable.  The hardware should only generate
> interrupts if you enable it (which should be always) AND when a thread
> tries to use the FPU... that way an application can enable or disable this
> mode automatically.  My experience is that if you allow someone to
> configure it, they'll mess it up, and that two years later, when a
> customer says, 'well, I only want to perform one operation...' that you
> don't have to rebuild the OS...

I thought the configurability was going to be between "make it always save
the FPU state", and "make it save the FPU state lazily". No application
would stop working as a result, if that's what you mean.

But if it isn't what you mean, I would say that there *is* extra overhead
in using lazy FPU switches so even if it's the default, having an
alternative is A Good Thing.

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