Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 7355690e authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
Browse files

[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: default avatarIngo 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>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3f555c70

kernel/sched.c

+1 −1
Original line number Diff line number Diff line
@@ -3547,7 +3547,7 @@ asmlinkage void __sched schedule(void) 
		}

	}

	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)