Commit-ID: a1e01829796aa7a993e28ffd7fee5c8d525be175
Gitweb: http://git.kernel.org/tip/a1e01829796aa7a993e28ffd7fee5c8d525be175
Author: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
AuthorDate: Wed, 20 Aug 2014 13:47:50 +0400
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 20 Aug 2014 14:53:02 +0200
sched: Remove double_rq_lock() from __migrate_task()
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@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mike Galbraith <umgwanakikbuti@xxxxxxxxx>
Cc: Kirill Tkhai <tkhai@xxxxxxxxx>
Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
Cc: Nicolas Pitre <nicolas.pitre@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1408528070.23412.89.camel@tkhai
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/core.c | 23 +++++++++++++++--------
1 file changed, 15 insertions(+), 8 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 71b8360..a773c91 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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;
}
--
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