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sched/fair: Fix entity's lag with run to parity

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When an entity is enqueued without preempting current, we must ensure
that the slice protection is updated to take into account the slice
duration of the newly enqueued task so that its lag will not exceed
its slice (+ tick).

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250708165630.1948751-6-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot 2025-07-08 18:56:29 +02:00 committed by Peter Zijlstra
parent 052c3d87c8
commit 3a0baa8e6c
1 changed files with 13 additions and 3 deletions
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16
kernel/sched/fair.c
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@ -889,13 +889,13 @@ struct sched_entity *__pick_first_entity(struct cfs_rq *cfs_rq)
* 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)
static inline void set_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
u64 slice = normalized_sysctl_sched_base_slice;
u64 vprot = se->deadline;
if (sched_feat(RUN_TO_PARITY))
slice = cfs_rq_min_slice(cfs_rq_of(se));
slice = cfs_rq_min_slice(cfs_rq);
slice = min(slice, se->slice);
if (slice != se->slice)
@ -904,6 +904,13 @@ static inline void set_protect_slice(struct sched_entity *se)
se->vprot = vprot;
}
static inline void update_protect_slice(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
u64 slice = cfs_rq_min_slice(cfs_rq);
se->vprot = min_vruntime(se->vprot, se->vruntime + calc_delta_fair(slice, se));
}
static inline bool protect_slice(struct sched_entity *se)
{
return ((s64)(se->vprot - se->vruntime) > 0);
@ -5467,7 +5474,7 @@ set_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *se)
__dequeue_entity(cfs_rq, se);
update_load_avg(cfs_rq, se, UPDATE_TG);
set_protect_slice(se);
set_protect_slice(cfs_rq, se);
}
update_stats_curr_start(cfs_rq, se);
@ -8720,6 +8727,9 @@ static void check_preempt_wakeup_fair(struct rq *rq, struct task_struct *p, int
if (__pick_eevdf(cfs_rq, !do_preempt_short) == pse)
goto preempt;
if (sched_feat(RUN_TO_PARITY) && do_preempt_short)
update_protect_slice(cfs_rq, se);
return;
preempt: