blob: 06e1e5d265d59b0e2e840e497efd6c16fcb64285 [file] [log] [blame]
From stable-bounces@linux.kernel.org Thu Mar 1 16:00:18 2007
From: Ingo Molnar <mingo@elte.hu>
Date: Thu, 01 Mar 2007 18:58:51 -0500
Subject: sched: fix SMT scheduler bug
To: linux-stable <stable@kernel.org>
Message-ID: <45E768BB.6050500@redhat.com>
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)