From: Peter Zijlstra <a.p.zijlstra@chello.nl>
Date: Tue, 5 Apr 2011 15:23:51 +0000 (+0200)
Subject: sched: Add p->pi_lock to task_rq_lock()
X-Git-Tag: v3.0-rc1~357^2~2^2~7
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0122ec5b02f76;p=pandora-kernel.git

sched: Add p->pi_lock to task_rq_lock()

In order to be able to call set_task_cpu() while either holding
p->pi_lock or task_rq(p)->lock we need to hold both locks in order to
stabilize task_rq().

This makes task_rq_lock() acquire both locks, and have
__task_rq_lock() validate that p->pi_lock is held. This increases the
locking overhead for most scheduler syscalls but allows reduction of
rq->lock contention for some scheduler hot paths (ttwu).

Reviewed-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Nick Piggin <npiggin@kernel.dk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20110405152729.232781355@chello.nl
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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