[PATCH 2/2] sched/fair: completely remove update_cfs_group() from enqueue path

[Aaron Lu]

---
 kernel/sched/fair.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index a21ab72819ce..8fc325112282 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4847,8 +4847,6 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
 	 */
 	update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH);
 	se_update_runnable(se);
-	if (cfs_rq->nr_running > 0)
-		update_cfs_group(se);
 	account_entity_enqueue(cfs_rq, se);
 
 	if (flags & ENQUEUE_WAKEUP)
@@ -6344,7 +6342,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 
 		update_load_avg(cfs_rq, se, UPDATE_TG);
 		se_update_runnable(se);
-		update_cfs_group(se);
 
 		cfs_rq->h_nr_running++;
 		cfs_rq->idle_h_nr_running += idle_h_nr_running;
-- 
2.40.1

Then P50's latency will bump to ~4ms from ~20us:
Latency percentiles (usec) runtime 300 (s) (17940 total samples)
        50.0th: 3996 (12092 samples)
        75.0th: 4004 (4919 samples)
        90.0th: 4004 (0 samples)
        95.0th: 4012 (353 samples)
        *99.0th: 20000 (487 samples)
        99.5th: 20000 (0 samples)
        99.9th: 31136 (72 samples)
        min=7, max=37402
real    5m36.633s
user    47m33.947s
sys     4m47.097s

So for the read side, maybe just keep what patch4 does?

Thanks,
Aaron