Commit-ID: c249f255aab86b9b187ba319b9d2684841ac7c8d Gitweb: http://git.kernel.org/tip/c249f255aab86b9b187ba319b9d2684841ac7c8d Author: Dave Kleikamp <[email protected]> AuthorDate: Mon, 15 May 2017 14:14:13 -0500 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 23 May 2017 10:01:34 +0200
sched/rt: Minimize rq->lock contention in do_sched_rt_period_timer() With CONFIG_RT_GROUP_SCHED=y, 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. Signed-off-by: Dave Kleikamp <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[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 c18b500..581d5c7 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) {
