Commit 9d514262 authored May 13, 2015 by Wanpeng Li Committed by Ingo Molnar Jun 19, 2015

sched/deadline: Reduce rq lock contention by eliminating locking of non-feasible target



This patch adds a check that prevents futile attempts to move DL tasks
to a CPU with active tasks of equal or earlier deadline. The same
behavior as commit 80e3d87b ("sched/rt: Reduce rq lock contention
by eliminating locking of non-feasible target") for rt class.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juri Lelli <juri.lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1431496867-4194-3-git-send-email-wanpeng.li@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent a6c0e746

kernel/sched/deadline.c

+14 −1

Original line number	Diff line number	Diff line
		@@ -1012,7 +1012,9 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags)
		(p->nr_cpus_allowed > 1)) {
		int target = find_later_rq(p);

		if (target != -1)
		if (target != -1 &&
		dl_time_before(p->dl.deadline,
		cpu_rq(target)->dl.earliest_dl.curr))
		cpu = target;
		}
		rcu_read_unlock();
		@@ -1359,6 +1361,17 @@ static struct rq find_lock_later_rq(struct task_struct task, struct rq *rq)

		later_rq = cpu_rq(cpu);

		if (!dl_time_before(task->dl.deadline,
		later_rq->dl.earliest_dl.curr)) {
		/*
		* Target rq has tasks of equal or earlier deadline,
		* retrying does not release any lock and is unlikely
		* to yield a different result.
		*/
		later_rq = NULL;
		break;
		}

		/* Retry if something changed. */
		if (double_lock_balance(rq, later_rq)) {
		if (unlikely(task_rq(task) != rq \|\|