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sched/core: Add ENQUEUE_RQ_SELECTED to indicate whether ->select_task_rq() was called

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During ttwu, ->select_task_rq() can be skipped if only one CPU is allowed or
migration is disabled. sched_ext schedulers may perform operations such as
direct dispatch from ->select_task_rq() path and it is useful for them to
know whether ->select_task_rq() was skipped in the ->enqueue_task() path.

Currently, sched_ext schedulers are using ENQUEUE_WAKEUP for this purpose
and end up assuming incorrectly that ->select_task_rq() was called for tasks
that are bound to a single CPU or migration disabled.

Make select_task_rq() indicate whether ->select_task_rq() was called by
setting WF_RQ_SELECTED in *wake_flags and make ttwu_do_activate() map that
to ENQUEUE_RQ_SELECTED for ->enqueue_task().

This will be used by sched_ext to fix ->select_task_rq() skip detection.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: David Vernet <void@manifault.com>
This commit is contained in:
Tejun Heo 2024-09-27 13:46:12 -10:00
parent b62933eee4
commit f207dc2dcd
2 changed files with 9 additions and 2 deletions
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8
kernel/sched/core.c
View File

@ -3522,10 +3522,12 @@ int select_task_rq(struct task_struct *p, int cpu, int *wake_flags)
{
lockdep_assert_held(&p->pi_lock);
if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p))
if (p->nr_cpus_allowed > 1 && !is_migration_disabled(p)) {
cpu = p->sched_class->select_task_rq(p, cpu, *wake_flags);
else
*wake_flags |= WF_RQ_SELECTED;
} else {
cpu = cpumask_any(p->cpus_ptr);
}
/*
* In order not to call set_task_cpu() on a blocking task we need
@ -3659,6 +3661,8 @@ ttwu_do_activate(struct rq *rq, struct task_struct *p, int wake_flags,
rq->nr_uninterruptible--;
#ifdef CONFIG_SMP
if (wake_flags & WF_RQ_SELECTED)
en_flags |= ENQUEUE_RQ_SELECTED;
if (wake_flags & WF_MIGRATED)
en_flags |= ENQUEUE_MIGRATED;
else

3
kernel/sched/sched.h
View File

@ -2292,6 +2292,7 @@ static inline int task_on_rq_migrating(struct task_struct *p)
#define WF_SYNC 0x10 /* Waker goes to sleep after wakeup */
#define WF_MIGRATED 0x20 /* Internal use, task got migrated */
#define WF_CURRENT_CPU 0x40 /* Prefer to move the wakee to the current CPU. */
#define WF_RQ_SELECTED 0x80 /* ->select_task_rq() was called */
#ifdef CONFIG_SMP
static_assert(WF_EXEC == SD_BALANCE_EXEC);
@ -2334,6 +2335,7 @@ extern const u32 sched_prio_to_wmult[40];
* ENQUEUE_HEAD - place at front of runqueue (tail if not specified)
* ENQUEUE_REPLENISH - CBS (replenish runtime and postpone deadline)
* ENQUEUE_MIGRATED - the task was migrated during wakeup
* ENQUEUE_RQ_SELECTED - ->select_task_rq() was called
*
*/
@ -2360,6 +2362,7 @@ extern const u32 sched_prio_to_wmult[40];
#define ENQUEUE_INITIAL 0x80
#define ENQUEUE_MIGRATING 0x100
#define ENQUEUE_DELAYED 0x200
#define ENQUEUE_RQ_SELECTED 0x400
#define RETRY_TASK ((void *)-1UL)