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[Xen-devel] Re: [PATCH] sched: provide scheduler_ipi() callback in respo

To: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] sched: provide scheduler_ipi() callback in response to smp_send_reschedule()
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon, 17 Jan 2011 21:43:03 +0100
Cc: linux-m32r-ja@xxxxxxxxxxxxxxxxx, linux-mips@xxxxxxxxxxxxxx, linux-m32r@xxxxxxxxxxxxxxxxx, linux-ia64@xxxxxxxxxxxxxxx, linux-sh@xxxxxxxxxxxxxxx, Heiko Carstens <heiko.carstens@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, Howells <dhowells@xxxxxxxxxx>, Paul Mackerras <paulus@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, sparclinux@xxxxxxxxxxxxxxx, Linux-Arch <linux-arch@xxxxxxxxxxxxxxx>, linux-s390@xxxxxxxxxxxxxxx, Jesper Nilsson <jesper.nilsson@xxxxxxxx>, Mikael, Russell King <linux@xxxxxxxxxxxxxxxx>, Takata <takata@xxxxxxxxxxxxxx>, x86@xxxxxxxxxx, "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Ingo Molnar <mingo@xxxxxxxxxx>, Chris, Matt Turner <mattst88@xxxxxxxxx>, uclinux-dist-devel@xxxxxxxxxxxxxxxxxxxx, Fenghua Yu <fenghua.yu@xxxxxxxxx>, Mike Frysinger <vapier@xxxxxxxxxx>, user-mode-linux-devel@xxxxxxxxxxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, Jeff Dike <jdike@xxxxxxxxxxx>, Metcalf <cmetcalf@xxxxxxxxxx>, David, Starvik <starvik@xxxxxxxx>, Schwidefsky <schwidefsky@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Ivan Kokshaysky <ink@xxxxxxxxxxxxxxxxxxxx>, user-mode-linux-user@xxxxxxxxxxxxxxxxxxxxx, Martin, Gleixner <tglx@xxxxxxxxxxxxx>, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx, Richard Henderson <rth@xxxxxxxxxxx>, Thomas, Luck <tony.luck@xxxxxxxxx>, linux-parisc@xxxxxxxxxxxxxxx, linux-cris-kernel@xxxxxxxx, Hirokazu, linux-am33-list@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, Ralf Baechle <ralf@xxxxxxxxxxxxxx>, "David S. Miller" <davem@xxxxxxxxxxxxx>, Kyle McMartin <kyle@xxxxxxxxxxx>, Paul Mundt <lethal@xxxxxxxxxxxx>, linux-alpha@xxxxxxxxxxxxxxx, Tony, linux390@xxxxxxxxxx, Koichi Yasutake <yasutake.koichi@xxxxxxxxxxxxxxxx>, linuxppc-dev@xxxxxxxxxxxxxxxx, Helge Deller <deller@xxxxxx>
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On Tue, 2011-01-18 at 07:31 +1100, Benjamin Herrenschmidt wrote:
> Beware of false positive, I've used "fake" reschedule IPIs in the past
> for other things (like kicking a CPU out of sleep state for unrelated
> reasons). Nothing that I know that is upstream today but some of that
> might come back. I'd like to avoid having to add an atomic to know if
> it's a real reschedule, will the scheduler be smart enough to not bother
> with false positives ? 

Yes it can deal with that, some will be for reschedules, some will be
for ttwu tail ends and x86 too uses this ipi for a few random other
things like kicking kvm out of guest context..

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