Commit 74eec636 authored by Vincent Guittot's avatar Vincent Guittot Committed by Peter Zijlstra
Browse files

sched/fair: Fix NO_RUN_TO_PARITY case 



EEVDF expects the scheduler to allocate a time quantum to the selected
entity and then pick a new entity for next quantum.
Although this notion of time quantum is not strictly doable in our case,
we can ensure a minimum runtime for each task most of the time and pick a
new entity after a minimum time has elapsed.
Reuse the slice protection of run to parity to ensure such runtime
quantum.

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-3-vincent.guittot@linaro.org
parent 9cdb4fe2

include/linux/sched.h

+9 −1
Original line number Diff line number Diff line
@@ -583,7 +583,15 @@ struct sched_entity { 
	u64				sum_exec_runtime;

	u64				prev_sum_exec_runtime;

	u64				vruntime;

	union {

		/*

		 * When !@on_rq this field is vlag.

		 * When cfs_rq->curr == se (which implies @on_rq)

		 * this field is vprot. See protect_slice().

		 */

		s64                     vlag;

		u64                     vprot;

	};

	u64				slice;



	u64				nr_migrations;

kernel/sched/fair.c

+20 −11
Original line number Diff line number Diff line
@@ -882,23 +882,35 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq) 
}



/*

 * HACK, stash a copy of deadline at the point of pick in vlag,

 * which isn't used until dequeue.

 * Set the vruntime up to which an entity can run before looking

 * for another entity to pick.

 * In case of run to parity, we protect the entity up to its deadline.

 * When run to parity is disabled, we give a minimum quantum to the running

 * entity to ensure progress.

 */

static inline void set_protect_slice(struct sched_entity *se)

{

	se->vlag = se->deadline;

	u64 slice = se->slice;

	u64 vprot = se->deadline;



	if (!sched_feat(RUN_TO_PARITY))

		slice = min(slice, normalized_sysctl_sched_base_slice);



	if (slice != se->slice)

		vprot = min_vruntime(vprot, se->vruntime + calc_delta_fair(slice, se));



	se->vprot = vprot;

}



static inline bool protect_slice(struct sched_entity *se)

{

	return se->vlag == se->deadline;

	return ((s64)(se->vprot - se->vruntime) > 0);

}



static inline void cancel_protect_slice(struct sched_entity *se)

{

	if (protect_slice(se))

		se->vlag = se->deadline + 1;

		se->vprot = se->vruntime;

}



/*
@@ -937,7 +949,7 @@ static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq) 
	if (curr && (!curr->on_rq || !entity_eligible(cfs_rq, curr)))

		curr = NULL;



	if (sched_feat(RUN_TO_PARITY) && curr && protect_slice(curr))

	if (curr && protect_slice(curr))

		return curr;



	/* Pick the leftmost entity if it's eligible */
@@ -1156,11 +1168,8 @@ static inline void update_curr_task(struct task_struct *p, s64 delta_exec) 
	cgroup_account_cputime(p, delta_exec);

}



static inline bool did_preempt_short(struct cfs_rq *cfs_rq, struct sched_entity *curr)

static inline bool resched_next_slice(struct cfs_rq *cfs_rq, struct sched_entity *curr)

{

	if (!sched_feat(PREEMPT_SHORT))

		return false;



	if (protect_slice(curr))

		return false;
@@ -1248,7 +1257,7 @@ static void update_curr(struct cfs_rq *cfs_rq) 
	if (cfs_rq->nr_queued == 1)

		return;



	if (resched || did_preempt_short(cfs_rq, curr)) {

	if (resched || resched_next_slice(cfs_rq, curr)) {

		resched_curr_lazy(rq);

		clear_buddies(cfs_rq, curr);

	}