Commit 8b5e770e authored May 13, 2015 by Wanpeng Li Committed by Ingo Molnar Jun 19, 2015

sched/deadline: Optimize pull_dl_task()



pull_dl_task() uses pick_next_earliest_dl_task() to select a migration
candidate; this is sub-optimal since the next earliest task -- as per
the regular runqueue -- might not be migratable at all. This could
result in iterating the entire runqueue looking for a task.

Instead iterate the pushable queue -- this queue only contains tasks
that have at least 2 cpus set in their cpus_allowed mask.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
[ Improved the changelog. ]
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/1431496867-4194-1-git-send-email-wanpeng.li@linux.intel.com


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

parent 1cde2930

kernel/sched/deadline.c

+27 −1

Original line number	Diff line number	Diff line
		@@ -1230,6 +1230,32 @@ static struct task_struct pick_next_earliest_dl_task(struct rq rq, int cpu)
		return NULL;
		}

		/*
		* Return the earliest pushable rq's task, which is suitable to be executed
		* on the CPU, NULL otherwise:
		*/
		static struct task_struct pick_earliest_pushable_dl_task(struct rq rq, int cpu)
		{
		struct rb_node *next_node = rq->dl.pushable_dl_tasks_leftmost;
		struct task_struct *p = NULL;

		if (!has_pushable_dl_tasks(rq))
		return NULL;

		next_node:
		if (next_node) {
		p = rb_entry(next_node, struct task_struct, pushable_dl_tasks);

		if (pick_dl_task(rq, p, cpu))
		return p;

		next_node = rb_next(next_node);
		goto next_node;
		}

		return NULL;
		}

		static DEFINE_PER_CPU(cpumask_var_t, local_cpu_mask_dl);

		static int find_later_rq(struct task_struct *task)
		@@ -1514,7 +1540,7 @@ static int pull_dl_task(struct rq *this_rq)
		if (src_rq->dl.dl_nr_running <= 1)
		goto skip;

		p = pick_next_earliest_dl_task(src_rq, this_cpu);
		p = pick_earliest_pushable_dl_task(src_rq, this_cpu);

		/*
		* We found a task to be pulled if: