Re: [PATCH] Extend mwait idle to optimize away CAL and RESinterrupts to an idle CPU -v1

[Peter Zijlstra]

On Thu, 2012-02-23 at 11:34 -0800, Venki Pallipadi wrote:

> > > +             local_bh_disable();
> > > +             local_irq_disable();
> >
> > That local_bh_disable() is completely superfluous, disabling IRQs
> > already kills bh.
> 
> The reason for local_bh_disable/enable was to check for potential
> softirqs after these interrupt.

Why is that needed? We never wrap local_irq_disable() in bh muck?


> > Why doesn't ipiless_idle_exit() call this? That would keep it isolated
> > to just those idle routines that actually use mwait instead of bothering
> > the generic idle paths with this.
> 
> ipiless_idle_exit is called in the inner most part of idle entry exit.
> In mwait case we may not even have interrupts enabled at that time and
> there is code that does idle residency timing etc which will get
> impacted if we start doing the pending ipi work there. Doing it at
> higher level along with things like enter-exit tickless felt nicer.

But but but, an actual interrupt can be handled before the instruction
after mwait, so why would this be a problem?

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