From: Ingo Molnar <[EMAIL PROTECTED]>
[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 <[EMAIL PROTECTED]>
Cc: Michal Piotrowski <[EMAIL PROTECTED]>
Cc: Nick Piggin <[EMAIL PROTECTED]>
Cc: Thomas Gleixner <[EMAIL PROTECTED]>
Cc: Chuck Ebbert <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
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)
--
-
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