Messages in this thread Patch in this message | | | Date | Fri, 6 May 2016 13:31:54 +0200 | From | Ingo Molnar <> | Subject | [GIT PULL] scheduler fix |
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Linus,
Please pull the latest sched-urgent-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus
# HEAD: 2548d546d40c0014efdde88a53bf7896e917dcce nohz/full, sched/rt: Fix missed tick-reenabling bug in sched_can_stop_tick()
This tree contains a single fix that fixes a nohz tick stopping bug when mixed-poliocy SCHED_FIFO and SCHED_RR tasks are present on a runqueue.
Thanks,
Ingo
------------------> Peter Zijlstra (1): nohz/full, sched/rt: Fix missed tick-reenabling bug in sched_can_stop_tick()
kernel/sched/core.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 8b489fcac37b..d1f7149f8704 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -596,17 +596,8 @@ bool sched_can_stop_tick(struct rq *rq) return false; /* - * FIFO realtime policy runs the highest priority task (after DEADLINE). - * Other runnable tasks are of a lower priority. The scheduler tick - * isn't needed. - */ - fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running; - if (fifo_nr_running) - return true; - - /* - * Round-robin realtime tasks time slice with other tasks at the same - * realtime priority. + * If there are more than one RR tasks, we need the tick to effect the + * actual RR behaviour. */ if (rq->rt.rr_nr_running) { if (rq->rt.rr_nr_running == 1) @@ -615,8 +606,20 @@ bool sched_can_stop_tick(struct rq *rq) return false; } - /* Normal multitasking need periodic preemption checks */ - if (rq->cfs.nr_running > 1) + /* + * If there's no RR tasks, but FIFO tasks, we can skip the tick, no + * forced preemption between FIFO tasks. + */ + fifo_nr_running = rq->rt.rt_nr_running - rq->rt.rr_nr_running; + if (fifo_nr_running) + return true; + + /* + * If there are no DL,RR/FIFO tasks, there must only be CFS tasks left; + * if there's more than one we need the tick for involuntary + * preemption. + */ + if (rq->nr_running > 1) return false; return true;
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