sched/fair: Merge for each idle cpu loop of ILB

Remove the specific case for handling this_cpu outside for_each_cpu() loop
when running ILB. Instead we use for_each_cpu_wrap() and start with the
next cpu after this_cpu so we will continue to finish with this_cpu.

update_nohz_stats() is now used for this_cpu too and will prevents
unnecessary update. We don't need a special case for handling the update of
nohz.next_balance for this_cpu anymore because it is now handled by the
loop like others.
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Link: https://lkml.kernel.org/r/20210224133007.28644-5-vincent.guittot@linaro.org

kernel/sched/fair.c

@@ -10043,22 +10043,9 @@ static void rebalance_domains(struct rq *rq, enum cpu_idle_type idle)
 	 * When the cpu is attached to null domain for ex, it will not be
 	 * updated.
 	 */
-	if (likely(update_next_balance)) {
+	if (likely(update_next_balance))
 		rq->next_balance = next_balance;
 
-#ifdef CONFIG_NO_HZ_COMMON
-		/*
-		 * If this CPU has been elected to perform the nohz idle
-		 * balance. Other idle CPUs have already rebalanced with
-		 * nohz_idle_balance() and nohz.next_balance has been
-		 * updated accordingly. This CPU is now running the idle load
-		 * balance for itself and we need to update the
-		 * nohz.next_balance accordingly.
-		 */
-		if ((idle == CPU_IDLE) && time_after(nohz.next_balance, rq->next_balance))
-			nohz.next_balance = rq->next_balance;
-#endif
-	}
 }
 
 static inline int on_null_domain(struct rq *rq)
@@ -10385,8 +10372,12 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
 	 */
 	smp_mb();
 
-	for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
-		if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
+	/*
+	 * Start with the next CPU after this_cpu so we will end with this_cpu and let a
+	 * chance for other idle cpu to pull load.
+	 */
+	for_each_cpu_wrap(balance_cpu,  nohz.idle_cpus_mask, this_cpu+1) {
+		if (!idle_cpu(balance_cpu))
 			continue;
 
 		/*
@@ -10432,15 +10423,6 @@ static void _nohz_idle_balance(struct rq *this_rq, unsigned int flags,
 	if (likely(update_next_balance))
 		nohz.next_balance = next_balance;
 
-	/* Newly idle CPU doesn't need an update */
-	if (idle != CPU_NEWLY_IDLE) {
-		update_blocked_averages(this_cpu);
-		has_blocked_load |= this_rq->has_blocked_load;
-	}
-
-	if (flags & NOHZ_BALANCE_KICK)
-		rebalance_domains(this_rq, CPU_IDLE);
-
 	WRITE_ONCE(nohz.next_blocked,
 		now + msecs_to_jiffies(LOAD_AVG_PERIOD));