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sched: Teach dequeue_task() about special task states

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Since special task states must not suffer spurious wakeups, and the
proposed delayed dequeue can cause exactly these (under some boundary
conditions), propagate this knowledge into dequeue_task() such that it
can do the right thing.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: Valentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105030.110439521@infradead.org
This commit is contained in:
Peter Zijlstra 2024-07-01 21:38:11 +02:00
parent a1c446611e
commit e1459a50ba
2 changed files with 8 additions and 2 deletions
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7
kernel/sched/core.c
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@ -6530,11 +6530,16 @@ static void __sched notrace __schedule(unsigned int sched_mode)
if (signal_pending_state(prev_state, prev)) {
WRITE_ONCE(prev->__state, TASK_RUNNING);
} else {
int flags = DEQUEUE_NOCLOCK;
prev->sched_contributes_to_load =
(prev_state & TASK_UNINTERRUPTIBLE) &&
!(prev_state & TASK_NOLOAD) &&
!(prev_state & TASK_FROZEN);
if (unlikely(is_special_task_state(prev_state)))
flags |= DEQUEUE_SPECIAL;
/*
* __schedule() ttwu()
* prev_state = prev->state; if (p->on_rq && ...)
@ -6546,7 +6551,7 @@ static void __sched notrace __schedule(unsigned int sched_mode)
*
* After this, schedule() must not care about p->state any more.
*/
block_task(rq, prev, DEQUEUE_NOCLOCK);
block_task(rq, prev, flags);
}
switch_count = &prev->nvcsw;
}

3
kernel/sched/sched.h
View File

@ -2248,10 +2248,11 @@ extern const u32 sched_prio_to_wmult[40];
*
*/
#define DEQUEUE_SLEEP 0x01
#define DEQUEUE_SLEEP 0x01 /* Matches ENQUEUE_WAKEUP */
#define DEQUEUE_SAVE 0x02 /* Matches ENQUEUE_RESTORE */
#define DEQUEUE_MOVE 0x04 /* Matches ENQUEUE_MOVE */
#define DEQUEUE_NOCLOCK 0x08 /* Matches ENQUEUE_NOCLOCK */
#define DEQUEUE_SPECIAL 0x10
#define DEQUEUE_MIGRATING 0x100 /* Matches ENQUEUE_MIGRATING */
#define DEQUEUE_DELAYED 0x200 /* Matches ENQUEUE_DELAYED */