On Wed, 2010-04-07 at 00:06 -0700, David Miller wrote:
> From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Date: Wed, 07 Apr 2010 08:52:26 +0200
>
> > On Tue, 2010-04-06 at 16:39 -0700, David Miller wrote:
> >> @@ -49,6 +49,16 @@ static inline void raw_local_irq_disable(void)
> >> );
> >> }
> >>
> >> +static inline void raw_local_irq_disable_nmi(void)
> >> +{
> >> + __asm__ __volatile__(
> >> + "wrpr %0, %%pil"
> >> + : /* no outputs */
> >> + : "i" (PIL_NMI)
> >> + : "memory"
> >> + );
> >> +}
> >> +
> >
> > Isn't this wrong when used from !NMI context?
> >
> > Should this thing do something like:
> >
> > if (rdpr() < PIL_NORMAL_MAX)
> > wrpr(PIL_NORMAL_MAX);
> >
> > so that it only disables IRQs, but doesn't enable NMIs.
>
> It's immaterial, local_irq_restore() will do the right thing,
> and it's ok to disable NMIs in these few cases I think.
>
> I desperately want to avoid that "test and maybe change the
> value %pil value we write" business, and honestly that's
> the whole point of this exercise.
Sure, its your architecture.. but could you explain why you're trying to
avoid that compare so desperately, the local_irq_save_nmi() calls are
few so surely they could carry that overhead.
Also, doesn't __raw_local_irq_save_flags() already do the read? So its
really just the compare that's gone missing.
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