On Mon, Feb 16, 2015 at 03:23:49PM -0500, Rik van Riel wrote: > If the CPU is running a realtime task that does not round-robin with > another realtime task of equal priority, there is no point in keeping > the scheduler tick going. After all, whenever the scheduler tick runs, > the kernel will just decide not to reschedule. > > Extend sched_can_stop_tick to recognize these situations, and inform > the rest of the kernel that the scheduler tick can be stopped. > > Signed-off-by: Rik van Riel <[email protected]> > Tested-by: Luiz Capitulino <[email protected]> > --- > kernel/sched/core.c | 16 ++++++++++++++++ > 1 file changed, 16 insertions(+) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index ade2958a9197..ad985a632c4d 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -745,6 +745,22 @@ static inline bool got_nohz_idle_kick(void) > bool sched_can_stop_tick(void) > { > /* > + * FIFO realtime policy runs the highest priority task. Other runnable > + * tasks are of a lower priority. The scheduler tick does nothing. > + */ > + if (current->policy == SCHED_FIFO) > + return true; > + > + /* > + * Round-robin realtime tasks time slice with other tasks at the same > + * realtime priority. Is this task the only one at this priority? > + */ > + if (current->policy == SCHED_RR) { > + struct sched_rt_entity *rt_se = ¤t->rt; > + return rt_se->run_list.prev == rt_se->run_list.next; > + } > + > + /*
I think it should work yes. There are still many things, that the tick updates, which are broken without it (rq->rt_avg is supposed to be updated avery tick for example) but it goes way beyond the scope of this change since SCHED_FIFO tasks are already allowed to stop the tick when no SCHED_OTHER task is running so the problem is there already before this patch. So it's a welcome fix, thanks. > * More than one running task need preemption. > * nr_running update is assumed to be visible > * after IPI is sent from wakers. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
