From d499ac7a3681e270074e880879d0e0a5ad0849fa Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Thu, 1 Mar 2007 18:58:51 -0500 Subject: 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(-) (limited to 'kernel') diff --git a/kernel/sched.c b/kernel/sched.c index a5a0b610865f..62db30c73554 100644 --- a/kernel/sched.c +++ b/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) -- cgit v1.2.3