| 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) |