sched/eevdf: Clear buddies for preempt_short

next buddy should not prevent shorter slice preemption. Don't take buddy
into account when checking if shorter slice entity can preempt and clear it
if the entity with a shorter slice can preempt current.

Test on snapdragon rb5:
hackbench -T -p -l 16000000 -g 2 1> /dev/null &
hackbench runs in cgroup /test-A
cyclictest -t 1 -i 2777 -D 63 --policy=fair --mlock  -h 20000 -q
cyclictest runs in cgroup /test-B

                     tip/sched/core  tip/sched/core    +this patch
cyclictest slice  (ms) (default)2.8             8               8
hackbench slice   (ms) (default)2.8            20              20
Total Samples          |    22679           22595           22686
Average           (us) |       84              94(-12%)        59( 37%)
Median (P50)      (us) |       56              56(  0%)        56(  0%)
90th Percentile   (us) |       64              65(- 2%)        63(  3%)
99th Percentile   (us) |     1047            1273(-22%)        74( 94%)
99.9th Percentile (us) |     2431            4751(-95%)       663( 86%)
Maximum           (us) |     4694            8655(-84%)      3934( 55%)

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260410132321.2897789-1-vincent.guittot@linaro.org

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 12890ef16603bff822c5a8160bc2c2e2f9a40427..f179faf7a6a1e9afa9b7496798d7ba8954b70180 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1116,7 +1116,7 @@ static struct sched_entity *__pick_eevdf(struct cfs_rq *cfs_rq, bool protect)
        /*
         * Picking the ->next buddy will affect latency but not fairness.
         */
-       if (sched_feat(PICK_BUDDY) &&
+       if (sched_feat(PICK_BUDDY) && protect &&
            cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next)) {
                /* ->next will never be delayed */
                WARN_ON_ONCE(cfs_rq->next->sched_delayed);
@@ -9138,8 +9138,10 @@ pick:
        return;
 
 preempt:
-       if (preempt_action == PREEMPT_WAKEUP_SHORT)
+       if (preempt_action == PREEMPT_WAKEUP_SHORT) {
                cancel_protect_slice(se);
+               clear_buddies(cfs_rq, se);
+       }
 
        resched_curr_lazy(rq);
 }