With CONFIG_RT_GROUP_SCHED defined, do_sched_rt_period_timer() sequentially takes each cpu's rq->lock. On a large, busy system, the cumulative time it takes to acquire each lock can be excessive, even triggering a watchdog timeout.
If rt_rq_rt_time and rt_rq->rt_nr_running are both zero, this function does nothing while holding the lock, so don't bother taking it at all. Orabug: 25491970 Signed-off-by: Dave Kleikamp <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra <[email protected]> --- kernel/sched/rt.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 9f3e40226dec..ae4a8c529a02 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -840,6 +840,17 @@ static int do_sched_rt_period_timer(struct rt_bandwidth *rt_b, int overrun) int enqueue = 0; struct rt_rq *rt_rq = sched_rt_period_rt_rq(rt_b, i); struct rq *rq = rq_of_rt_rq(rt_rq); + int skip; + + /* + * When span == cpu_online_mask, taking each rq->lock + * can be time-consuming. Try to avoid it when possible. + */ + raw_spin_lock(&rt_rq->rt_runtime_lock); + skip = !rt_rq->rt_time && !rt_rq->rt_nr_running; + raw_spin_unlock(&rt_rq->rt_runtime_lock); + if (skip) + continue; raw_spin_lock(&rq->lock); if (rt_rq->rt_time) { -- 2.12.2
