Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit b18c3ca1 authored by Byungchul Park's avatar Byungchul Park Committed by Ingo Molnar
Browse files

sched/deadline: Make find_later_rq() choose a closer CPU in topology 



When cpudl_find() returns any among free_cpus, the CPU might not be
closer than others, considering sched domain. For example:

   this_cpu: 15
   free_cpus: 0, 1,..., 14 (== later_mask)
   best_cpu: 0

   topology:

   0 --+
       +--+
   1 --+  |
          +-- ... --+
   2 --+  |         |
       +--+         |
   3 --+            |

   ...             ...

   12 --+           |
        +--+        |
   13 --+  |        |
           +-- ... -+
   14 --+  |
        +--+
   15 --+

In this case, it would be best to select 14 since it's a free CPU and
closest to 15 (this_cpu). However, currently the code selects 0 (best_cpu)
even though that's just any among free_cpus. Fix it.

This (re)aligns the deadline behaviour with the rt behaviour.

Signed-off-by: default avatarByungchul Park <byungchul.park@lge.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: <bristot@redhat.com>
Cc: <juri.lelli@gmail.com>
Cc: <kernel-team@lge.com>
Cc: <rostedt@goodmis.org>
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/1495504859-10960-2-git-send-email-byungchul.park@lge.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent b5dd77c8

kernel/sched/deadline.c

+14 −13
Original line number Diff line number Diff line
@@ -1798,7 +1798,7 @@ static int find_later_rq(struct task_struct *task) 
	struct sched_domain *sd;

	struct cpumask *later_mask = this_cpu_cpumask_var_ptr(local_cpu_mask_dl);

	int this_cpu = smp_processor_id();

	int best_cpu, cpu = task_cpu(task);

	int cpu = task_cpu(task);



	/* Make sure the mask is initialized first */

	if (unlikely(!later_mask))
@@ -1811,17 +1811,14 @@ static int find_later_rq(struct task_struct *task) 
	 * We have to consider system topology and task affinity

	 * first, then we can look for a suitable cpu.

	 */

	best_cpu = cpudl_find(&task_rq(task)->rd->cpudl,

			task, later_mask);

	if (best_cpu == -1)

	if (cpudl_find(&task_rq(task)->rd->cpudl, task, later_mask) == -1)

		return -1;



	/*

	 * If we are here, some target has been found,

	 * the most suitable of which is cached in best_cpu.

	 * This is, among the runqueues where the current tasks

	 * have later deadlines than the task's one, the rq

	 * with the latest possible one.

	 * If we are here, some targets have been found, including

	 * the most suitable which is, among the runqueues where the

	 * current tasks have later deadlines than the task's one, the

	 * rq with the latest possible one.

	 *

	 * Now we check how well this matches with task's

	 * affinity and system topology.
@@ -1841,6 +1838,7 @@ static int find_later_rq(struct task_struct *task) 
	rcu_read_lock();

	for_each_domain(cpu, sd) {

		if (sd->flags & SD_WAKE_AFFINE) {

			int best_cpu;



			/*

			 * If possible, preempting this_cpu is
@@ -1852,12 +1850,15 @@ static int find_later_rq(struct task_struct *task) 
				return this_cpu;

			}



			best_cpu = cpumask_first_and(later_mask,

							sched_domain_span(sd));

			/*

			 * Last chance: if best_cpu is valid and is

			 * in the mask, that becomes our choice.

			 * Last chance: if a cpu being in both later_mask

			 * and current sd span is valid, that becomes our

			 * choice. Of course, the latest possible cpu is

			 * already under consideration through later_mask.

			 */

			if (best_cpu < nr_cpu_ids &&

			    cpumask_test_cpu(best_cpu, sched_domain_span(sd))) {

			if (best_cpu < nr_cpu_ids) {

				rcu_read_unlock();

				return best_cpu;

			}