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sched: Rework CPU hotplug task selection

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The CPU hotplug task selection is the only place where we used
put_prev_task() on a task that is not current. While looking at that,
it occured to me that we can simplify all that by by using a custom
pick loop.

Since we don't need to put current, we can do away with the fake task
too.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Aaron Lu <aaron.lwe@gmail.com>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: mingo@kernel.org
Cc: Phil Auld <pauld@redhat.com>
Cc: Julien Desfossez <jdesfossez@digitalocean.com>
Cc: Nishanth Aravamudan <naravamudan@digitalocean.com>
This commit is contained in:
Peter Zijlstra 2019-08-06 15:13:17 +02:00
parent f95d4eaee6
commit 10e7071b2f
2 changed files with 16 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
kernel/sched/core.c
View File

@ -6082,22 +6082,23 @@ static void calc_load_migrate(struct rq *rq)
atomic_long_add(delta, &calc_load_tasks);
}
static void put_prev_task_fake(struct rq *rq, struct task_struct *prev)
static struct task_struct *__pick_migrate_task(struct rq *rq)
{
const struct sched_class *class;
struct task_struct *next;
for_each_class(class) {
next = class->pick_next_task(rq, NULL, NULL);
if (next) {
next->sched_class->put_prev_task(rq, next);
return next;
}
}
/* The idle class should always have a runnable task */
BUG();
}
static const struct sched_class fake_sched_class = {
.put_prev_task = put_prev_task_fake,
};
static struct task_struct fake_task = {
/*
* Avoid pull_{rt,dl}_task()
*/
.prio = MAX_PRIO + 1,
.sched_class = &fake_sched_class,
};
/*
* Migrate all tasks from the rq, sleeping tasks will be migrated by
* try_to_wake_up()->select_task_rq().
@ -6139,12 +6140,7 @@ static void migrate_tasks(struct rq *dead_rq, struct rq_flags *rf)
if (rq->nr_running == 1)
break;
/*
* pick_next_task() assumes pinned rq->lock:
*/
next = pick_next_task(rq, &fake_task, rf);
BUG_ON(!next);
put_prev_task(rq, next);
next = __pick_migrate_task(rq);
/*
* Rules for changing task_struct::cpus_mask are holding

1
kernel/sched/sched.h
View File

@ -1751,6 +1751,7 @@ struct sched_class {
static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
{
WARN_ON_ONCE(rq->curr != prev);
prev->sched_class->put_prev_task(rq, prev);
}