RE: [Xen-ia64-devel] PATCH [resend]: more case handled in mmio.c

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

>From: Tristan Gingold
>Sent: 2006?4?14? 19:36
>To: xen-ia64-devel@xxxxxxxxxxxxxxxxxxx; Alex Williamson
>Subject: [Xen-ia64-devel] PATCH [resend]: more case handled in mmio.c
>
>Hi,
>
>thanks to Anthony comments, I have rewritten getfpregs.
>
>Tested by booting domVTI.

I don't think getfpreg will be executed even domVTI is booting. :-).

Currently, every time domain switch, all floating registers are saved.
So lazy floating registers save/restore algorithm is not implemented in xen.
It's not ease. :-).
When domain switch happens, below function is called.
/* load f32-f127 from FPH */
static inline void
ia64_load_fpu (struct ia64_fpreg *fph) {
        ia64_fph_enable();
        __ia64_load_fpu(fph);
        ia64_fph_disable();
}
Fph is disabled, and if getfpreg is called, disabled floating
Register fault may happen.
Because all fr are saved at domain switch, seems VMM don't
Need to disable fph.
My question is,
Do we need to implement lazy fr algorithm?
If yes, we need to handle disabled fr fault and not need to save
all fr at domain switch.
If no, we can simply remove all ia64_fph_enable() and ia64_fph_disable()
in VMM.
What's your option?


Thanks,
Anthony

>
>Tristan.

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