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>
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 890ce95..9cbe1c7 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1230,6 +1230,32 @@
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 @@
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: