Commit e1459a50 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched: Teach dequeue_task() about special task states 



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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <vschneid@redhat.com>
Tested-by: default avatarValentin Schneider <vschneid@redhat.com>
Link: https://lkml.kernel.org/r/20240727105030.110439521@infradead.org
parent a1c44661

kernel/sched/core.c

+6 −1
Original line number Diff line number Diff line
@@ -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;

	}

kernel/sched/sched.h

+2 −1
Original line number Diff line number Diff line
@@ -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 */