sched/fair: Fix effective_load() to consistently use smoothed load

Starting with the following commit:

  fde7d22e01 ("sched/fair: Fix overly small weight for interactive group entities")

calc_tg_weight() doesn't compute the right value as expected by effective_load().

The difference is in the 'correction' term. In order to ensure \Sum
rw_j >= rw_i we cannot use tg->load_avg directly, since that might be
lagging a correction on the current cfs_rq->avg.load_avg value.
Therefore we use tg->load_avg - cfs_rq->tg_load_avg_contrib +
cfs_rq->avg.load_avg.

Now, per the referenced commit, calc_tg_weight() doesn't use
cfs_rq->avg.load_avg, as is later used in @w, but uses
cfs_rq->load.weight instead.

So stop using calc_tg_weight() and do it explicitly.

The effects of this bug are wake_affine() making randomly
poor choices in cgroup-intense workloads.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org> # v4.3+
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: fde7d22e01 ("sched/fair: Fix overly small weight for interactive group entities")
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -735,8 +735,6 @@ void post_init_entity_util_avg(struct sched_entity *se)
 	}
 }
 
-static inline unsigned long cfs_rq_runnable_load_avg(struct cfs_rq *cfs_rq);
-static inline unsigned long cfs_rq_load_avg(struct cfs_rq *cfs_rq);
 #else
 void init_entity_runnable_average(struct sched_entity *se)
 {
@@ -4946,19 +4944,24 @@ static long effective_load(struct task_group *tg, int cpu, long wl, long wg)
 		return wl;
 
 	for_each_sched_entity(se) {
-		long w, W;
+		struct cfs_rq *cfs_rq = se->my_q;
+		long W, w = cfs_rq_load_avg(cfs_rq);
 
-		tg = se->my_q->tg;
+		tg = cfs_rq->tg;
 
 		/*
 		 * W = @wg + \Sum rw_j
 		 */
-		W = wg + calc_tg_weight(tg, se->my_q);
+		W = wg + atomic_long_read(&tg->load_avg);
+
+		/* Ensure \Sum rw_j >= rw_i */
+		W -= cfs_rq->tg_load_avg_contrib;
+		W += w;
 
 		/*
 		 * w = rw_i + @wl
 		 */
-		w = cfs_rq_load_avg(se->my_q) + wl;
+		w += wl;
 
 		/*
 		 * wl = S * s'_i; see (2)