Messages in this thread Patch in this message | | | Date | Wed, 07 Mar 2007 09:11:50 -0800 | From | Greg KH <> | Subject | [patch 075/101] sched: fix SMT scheduler bug |
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From: Ingo Molnar <mingo@elte.hu>
[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> Cc: Chuck Ebbert <cebbert@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
--- kernel/sched.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- linux-2.6.20.1.orig/kernel/sched.c +++ linux-2.6.20.1/kernel/sched.c @@ -3528,7 +3528,7 @@ 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) -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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