Re: [PATCH 4/4] sched,fair: Fix PELT integrity for new tasks

[Peter Zijlstra]

On Fri, Jun 17, 2016 at 06:02:39PM +0200, Peter Zijlstra wrote:
> So yes, ho-humm, how to go about doing that bestest. Lemme have a play.

This is what I came up with, not entirely pretty, but I suppose it'll
have to do.

---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -724,6 +724,7 @@ void post_init_entity_util_avg(struct sc
 	struct cfs_rq *cfs_rq = cfs_rq_of(se);
 	struct sched_avg *sa = &se->avg;
 	long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
+	u64 now = cfs_rq_clock_task(cfs_rq);
 
 	if (cap > 0) {
 		if (cfs_rq->avg.util_avg != 0) {
@@ -738,7 +739,20 @@ void post_init_entity_util_avg(struct sc
 		sa->util_sum = sa->util_avg * LOAD_AVG_MAX;
 	}
 
-	update_cfs_rq_load_avg(cfs_rq_clock_task(cfs_rq), cfs_rq, false);
+	if (entity_is_task(se)) {
+		struct task_struct *p = task_of(se);
+		if (p->sched_class != &fair_sched_class) {
+			/*
+			 * For !fair tasks do attach_entity_load_avg()
+			 * followed by detach_entity_load_avg() as per
+			 * switched_from_fair().
+			 */
+			se->avg.last_update_time = now;
+			return;
+		}
+	}
+
+	update_cfs_rq_load_avg(now, cfs_rq, false);
 	attach_entity_load_avg(cfs_rq, se);
 }