Re: [PATCH 0/2] sparc64: Use low latency path to resume idle cpu

[Vijay Kumar]

On 7/20/2017 9:55 PM, David Miller wrote:
> From: Vijay Kumar <vijay.ac.kumar@xxxxxxxxxx>
> Date: Thu, 20 Jul 2017 21:44:24 -0500
>
> > I had same thoughts initially but I had to go with this approach as
> > scheduler_ipi is wrapped with irq_enter() and irq_exit(). Whereas POKE
> > resumes the cpu in process context.
> >
> > Comments in scheduler_ipi():
> >
> >           * Not all reschedule IPI handlers call irq_enter/irq_exit, since
> >           * traditionally all their work was done from the interrupt return
> >           * path. Now that we actually do some work, we need to make sure
> >           * we do call them.
> >           *
> >           * Some archs already do call them, luckily irq_enter/exit nest
> >           * properly.
> >           *
> >           * Arguably we should visit all archs and update all handlers,
> >           * however a fair share of IPIs are still resched only so this would
> >           * somewhat pessimize the simple resched case.
> >           */
> >          irq_enter();
> I still think we should be able to fake the state such that this
> direct schedule_ipi() call will work.
>
> I could be wrong :)
I can give a try :). But looks to me one thing that will go wrong is irq 
accounting done in __irq_enter() and rcu_irq_enter().

Thanks,
Vijay