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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: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-3-vincent.guittot@linaro.org
pull/1309/head
Vincent Guittot 2025-07-08 18:56:26 +02:00 committed by Peter Zijlstra
parent 9cdb4fe20c
commit 74eec63661
2 changed files with 29 additions and 12 deletions
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10
include/linux/sched.h
View File

@ -583,7 +583,15 @@ struct sched_entity {
u64 sum_exec_runtime;
u64 prev_sum_exec_runtime;
u64 vruntime;
s64 vlag;
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;

31
kernel/sched/fair.c
View File

@ -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);
}