Commit e140749c authored by Valentin Schneider's avatar Valentin Schneider Committed by Ingo Molnar
Browse files

sched: Simplify migration_cpu_stop() 



Since, when ->stop_pending, only the stopper can uninstall
p->migration_pending. This could simplify a few ifs, because:

  (pending != NULL) => (pending == p->migration_pending)

Also, the fatty comment above affine_move_task() probably needs a bit
of gardening.

Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ce29ddc4

kernel/sched/core.c

+18 −9
Original line number Diff line number Diff line
@@ -1926,6 +1926,12 @@ static int migration_cpu_stop(void *data) 
	raw_spin_lock(&p->pi_lock);

	rq_lock(rq, &rf);



	/*

	 * If we were passed a pending, then ->stop_pending was set, thus

	 * p->migration_pending must have remained stable.

	 */

	WARN_ON_ONCE(pending && pending != p->migration_pending);



	/*

	 * If task_rq(p) != rq, it cannot be migrated here, because we're

	 * holding rq->lock, if p->on_rq == 0 it cannot get enqueued because
@@ -1936,7 +1942,6 @@ static int migration_cpu_stop(void *data) 
			goto out;



		if (pending) {

			if (p->migration_pending == pending)

			p->migration_pending = NULL;

			complete = true;

		}
@@ -1976,7 +1981,6 @@ static int migration_cpu_stop(void *data) 
		 * somewhere allowed, we're done.

		 */

		if (cpumask_test_cpu(task_cpu(p), p->cpus_ptr)) {

			if (p->migration_pending == pending)

			p->migration_pending = NULL;

			complete = true;

			goto out;
@@ -2165,16 +2169,21 @@ void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask) 
 *

 * (1) In the cases covered above. There is one more where the completion is

 * signaled within affine_move_task() itself: when a subsequent affinity request

 * cancels the need for an active migration. Consider:

 * occurs after the stopper bailed out due to the targeted task still being

 * Migrate-Disable. Consider:

 *

 *     Initial conditions: P0->cpus_mask = [0, 1]

 *

 *     P0@CPU0            P1                             P2

 *

 *     CPU0		  P1				P2

 *     <P0>

 *       migrate_disable();

 *       <preempted>

 *                        set_cpus_allowed_ptr(P0, [1]);

 *                          <blocks>

 *     <migration/0>

 *       migration_cpu_stop()

 *         is_migration_disabled()

 *           <bails>

 *                                                       set_cpus_allowed_ptr(P0, [0, 1]);

 *                                                         <signal completion>

 *                          <awakes>