Commit 7355690e authored Feb 28, 2007 by Ingo Molnar Committed by Linus Torvalds Mar 01, 2007

[PATCH] sched: fix SMT scheduler bug



The SMT scheduler incorrectly skips kernel threads even if they are
runnable (but they are preempted by a higher-prio user-space task which got
SMT-delayed by an even higher-priority task running on a sibling CPU).

Fix this for now by only doing the SMT-nice optimization if the
to-be-delayed task is the only runnable task.  (This should cover most of
the real-life cases anyway.)

This bug has been in the SMT scheduler since 2.6.17 or so, but has only
been noticed now by the active check in the dynticks code.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3f555c70

kernel/sched.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -3547,7 +3547,7 @@ need_resched_nonpreemptible:
		}
		}
		next->sleep_type = SLEEP_NORMAL;
		if (dependent_sleeper(cpu, rq, next))
		if (rq->nr_running == 1 && dependent_sleeper(cpu, rq, next))
		next = rq->idle;
		switch_tasks:
		if (next == rq->idle)

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