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Subject: Re: [PATCH] sched: provide scheduler_ipi() callback in response to
 smp_send_reschedule()
From:   Benjamin Herrenschmidt <benh@kernel.crashing.org>
To:     Peter Zijlstra <peterz@infradead.org>
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Date:   Wed, 09 Feb 2011 17:14:14 +1100
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On Mon, 2011-02-07 at 14:54 +0100, Peter Zijlstra wrote:
> On Mon, 2011-02-07 at 10:26 +1100, Benjamin Herrenschmidt wrote:
> > You missed:
> > 
> > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
> > index 9813605..467d122 100644
> > --- a/arch/powerpc/kernel/smp.c
> > +++ b/arch/powerpc/kernel/smp.c
> > @@ -98,6 +98,7 @@ void smp_message_recv(int msg)
> >                 break;
> >         case PPC_MSG_RESCHEDULE:
> >                 /* we notice need_resched on exit */
> > +               scheduler_ipi();
> >                 break;
> >         case PPC_MSG_CALL_FUNC_SINGLE:
> >                 generic_smp_call_function_single_interrupt();
> > 
> > Fold that in and add:
> > 
> > Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> 
> Thanks Ben!

BTW. I we lurking at some of our CPU hotplug code and I think I cannot
totally guarantee that this won't be called on an offline CPU. If that's
a problem, you may want to add a test for that.

IE. The call function IPIs are normally not going to be sent to an
offlined CPU, and stop_machine should be a good enough fence here, but
we do abuse reschedule for a number of things (including in some case
to wake up a sleeping CPU that was pseudo-offlined :-)

Cheers,
Ben.