[PATCH v3 3/4] sched/pelt: Relax the sync of runnable_sum with runnable_avg

From: Vincent Guittot
Date: Tue Jan 11 2022 - 08:47:31 EST


Similarly to util_avg and util_sum, don't sync runnable_sum with the low
bound of runnable_avg but only ensure that runnable_sum stays in the
correct range.

Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
kernel/sched/fair.c | 33 +++++++++++++++++++--------------
1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3eb73ce6ef13..e34de721a630 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3485,11 +3485,11 @@ update_tg_cfs_util(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq
static inline void
update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cfs_rq *gcfs_rq)
{
- long delta = gcfs_rq->avg.runnable_avg - se->avg.runnable_avg;
- u32 divider;
+ long delta_sum, delta_avg = gcfs_rq->avg.runnable_avg - se->avg.runnable_avg;
+ u32 new_sum, divider;

/* Nothing to update */
- if (!delta)
+ if (!delta_avg)
return;

/*
@@ -3500,11 +3500,16 @@ update_tg_cfs_runnable(struct cfs_rq *cfs_rq, struct sched_entity *se, struct cf

/* Set new sched_entity's runnable */
se->avg.runnable_avg = gcfs_rq->avg.runnable_avg;
- se->avg.runnable_sum = se->avg.runnable_avg * divider;
+ new_sum = se->avg.runnable_avg * divider;
+ delta_sum = (long)new_sum - (long)se->avg.runnable_sum;
+ se->avg.runnable_sum = new_sum;

/* Update parent cfs_rq runnable */
- add_positive(&cfs_rq->avg.runnable_avg, delta);
- cfs_rq->avg.runnable_sum = cfs_rq->avg.runnable_avg * divider;
+ add_positive(&cfs_rq->avg.runnable_avg, delta_avg);
+ add_positive(&cfs_rq->avg.runnable_sum, delta_sum);
+ /* See update_cfs_rq_load_avg() */
+ cfs_rq->avg.runnable_sum = max_t(u32, cfs_rq->avg.runnable_sum,
+ cfs_rq->avg.runnable_avg * MIN_DIVIDER);
}

static inline void
@@ -3704,7 +3709,10 @@ update_cfs_rq_load_avg(u64 now, struct cfs_rq *cfs_rq)

r = removed_runnable;
sub_positive(&sa->runnable_avg, r);
- sa->runnable_sum = sa->runnable_avg * divider;
+ sub_positive(&sa->runnable_sum, r * divider);
+ /* See sa->util_sum above */
+ sa->runnable_sum = max_t(u32, sa->runnable_sum,
+ sa->runnable_avg * MIN_DIVIDER);

/*
* removed_runnable is the unweighted version of removed_load so we
@@ -3791,12 +3799,6 @@ static void attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
*/
static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se)
{
- /*
- * cfs_rq->avg.period_contrib can be used for both cfs_rq and se.
- * See ___update_load_avg() for details.
- */
- u32 divider = get_pelt_divider(&cfs_rq->avg);
-
dequeue_load_avg(cfs_rq, se);
sub_positive(&cfs_rq->avg.util_avg, se->avg.util_avg);
sub_positive(&cfs_rq->avg.util_sum, se->avg.util_sum);
@@ -3805,7 +3807,10 @@ static void detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
cfs_rq->avg.util_avg * MIN_DIVIDER);

sub_positive(&cfs_rq->avg.runnable_avg, se->avg.runnable_avg);
- cfs_rq->avg.runnable_sum = cfs_rq->avg.runnable_avg * divider;
+ sub_positive(&cfs_rq->avg.runnable_sum, se->avg.runnable_sum);
+ /* See update_cfs_rq_load_avg() */
+ cfs_rq->avg.runnable_sum = max_t(u32, cfs_rq->avg.runnable_sum,
+ cfs_rq->avg.runnable_avg * MIN_DIVIDER);

add_tg_cfs_propagate(cfs_rq, -se->avg.load_sum);

--
2.17.1