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sched: Remove double_rq_lock() from __migrate_task()

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Avoid double_rq_lock() and use TASK_ON_RQ_MIGRATING for
__migrate_task(). The advantage is (obviously) not holding two
rq->lock's at the same time and thereby increasing parallelism.

The important point to note is that because we acquire dst->lock
immediately after releasing src->lock the potential wait time of
task_rq_lock() callers on TASK_ON_RQ_MIGRATING is not longer
than it would have been in the double rq lock scenario.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Turner <pjt@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Kirill Tkhai <tkhai@yandex.ru>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1408528070.23412.89.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Kirill Tkhai 2014-08-20 13:47:50 +04:00 committed by Ingo Molnar
parent cca26e8009
commit a1e0182979
1 changed files with 15 additions and 8 deletions
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23
kernel/sched/core.c
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@ -4679,20 +4679,20 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr);
*/
static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
{
struct rq *rq_dest, *rq_src;
struct rq *rq;
int ret = 0;
if (unlikely(!cpu_active(dest_cpu)))
return ret;
rq_src = cpu_rq(src_cpu);
rq_dest = cpu_rq(dest_cpu);
rq = cpu_rq(src_cpu);
raw_spin_lock(&p->pi_lock);
double_rq_lock(rq_src, rq_dest);
raw_spin_lock(&rq->lock);
/* Already moved. */
if (task_cpu(p) != src_cpu)
goto done;
/* Affinity changed (again). */
if (!cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))
goto fail;
@ -4702,15 +4702,22 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
* placed properly.
*/
if (task_on_rq_queued(p)) {
dequeue_task(rq_src, p, 0);
dequeue_task(rq, p, 0);
p->on_rq = TASK_ON_RQ_MIGRATING;
set_task_cpu(p, dest_cpu);
enqueue_task(rq_dest, p, 0);
check_preempt_curr(rq_dest, p, 0);
raw_spin_unlock(&rq->lock);
rq = cpu_rq(dest_cpu);
raw_spin_lock(&rq->lock);
BUG_ON(task_rq(p) != rq);
p->on_rq = TASK_ON_RQ_QUEUED;
enqueue_task(rq, p, 0);
check_preempt_curr(rq, p, 0);
}
done:
ret = 1;
fail:
double_rq_unlock(rq_src, rq_dest);
raw_spin_unlock(&rq->lock);
raw_spin_unlock(&p->pi_lock);
return ret;
}