From: Ingo Molnar [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 Cc: Michal Piotrowski Cc: Nick Piggin Cc: Thomas Gleixner Cc: Chuck Ebbert Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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/