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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Wed, 09 Feb 2011 17:14:14 +1100
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Subject: Re: [PATCH] sched: provide scheduler_ipi() callback in response to
 smp_send_reschedule()
To: Peter Zijlstra <peterz@infradead.org>
Cc: Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Russell King <linux@arm.linux.org.uk>, Mike Frysinger <vapier@gentoo.org>, Mikael Starvik <starvik@axis.com>, Jesper Nilsson <jesper.nilsson@axis.com>, Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>, Hirokazu Takata <takata@linux-m32r.org>, Ralf Baechle <ralf@linux-mips.org>, David Howells <dhowells@redhat.com>, Koichi Yasutake <yasutake.koichi@jp.panasonic.com>, Kyle McMartin <kyle@mcmartin.ca>, Helge Deller <deller@gmx.de>, "James E.J. Bottomley" <jejb@parisc-linux.org>, Paul Mackerras <paulus@samba.org>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Heiko Carstens <heiko.carstens@de.ibm.com>, linux390@de.ibm.com, Paul Mundt <lethal@linux-sh.org>, "David S. Miller" <davem@davemloft.net>, Chris Metcalf <cmetcalf@tilera.com>, Jeff Dike <jdike@addtoit.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org, Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, uclinux-dist-devel@blackfin.uclinux.org, linux-cris-kernel@axis.com, linux-ia64@vger.kernel.org, linux-m32r@ml.linux-m32r.org, linux-m32r-ja@ml.linux-m32r.org, linux-mips@linux-mips.org, linux-am33-list@redhat.com, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, user-mode-linux-user@lists.sourceforge.net, xen-devel@lists.xensource.com, virtualization@lists.osdl.org, Linux-Arch <linux-arch@vger.kernel.org>
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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.