[RFC PATCH 15/16 v3] Intercept periodic nohz idle balancing

[Yuyang Du]

We intercept load balancing to contain the load and load balancing in
the consolidated CPUs according to our consolidating mechanism.

In periodic nohz idle balance, we skip the idle but non-consolidated
CPUs from load balancing.

Signed-off-by: Yuyang Du <yuyang.du@xxxxxxxxx>
---
 kernel/sched/fair.c |   57 ++++++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 47 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 220773f..1b8dd45 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6869,10 +6869,47 @@ static struct {
 
 static inline int find_new_ilb(void)
 {
-	int ilb = cpumask_first(nohz.idle_cpus_mask);
+	int ilb;
 
-	if (ilb < nr_cpu_ids && idle_cpu(ilb))
-		return ilb;
+	/*
+	 * Optimize for the case when we have no idle CPUs or only one
+	 * idle CPU. Don't walk the sched_domain hierarchy in such cases
+	 */
+	if (cpumask_weight(nohz.idle_cpus_mask) < 2)
+		return nr_cpu_ids;
+
+	ilb = cpumask_first(nohz.idle_cpus_mask);
+
+	if (ilb < nr_cpu_ids && idle_cpu(ilb)) {
+		struct sched_domain *sd;
+		int this_cpu = smp_processor_id();
+
+		rcu_read_lock();
+		sd = top_flag_domain(this_cpu, SD_WORKLOAD_CONSOLIDATION);
+		if (sd) {
+			struct cpumask *nonshielded_cpus = __get_cpu_var(load_balance_mask);
+
+			cpumask_copy(nonshielded_cpus, nohz.idle_cpus_mask);
+
+			wc_nonshielded_mask(this_cpu, sd, nonshielded_cpus);
+			rcu_read_unlock();
+
+			if (cpumask_weight(nonshielded_cpus) < 2)
+				return nr_cpu_ids;
+
+			/*
+			 * get idle load balancer again
+			 */
+			ilb = cpumask_first(nonshielded_cpus);
+
+		    if (ilb < nr_cpu_ids && idle_cpu(ilb))
+				return ilb;
+		}
+		else {
+			rcu_read_unlock();
+			return ilb;
+		}
+	}
 
 	return nr_cpu_ids;
 }
@@ -7109,7 +7146,7 @@ out:
  * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the
  * rebalancing for all the cpus for whom scheduler ticks are stopped.
  */
-static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
+static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle, struct cpumask *mask)
 {
 	int this_cpu = this_rq->cpu;
 	struct rq *rq;
@@ -7119,7 +7156,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
 	    !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)))
 		goto end;
 
-	for_each_cpu(balance_cpu, nohz.idle_cpus_mask) {
+	for_each_cpu(balance_cpu, mask) {
 		if (balance_cpu == this_cpu || !idle_cpu(balance_cpu))
 			continue;
 
@@ -7167,10 +7204,10 @@ static inline int nohz_kick_needed(struct rq *rq)
 	if (unlikely(rq->idle_balance))
 		return 0;
 
-       /*
-	* We may be recently in ticked or tickless idle mode. At the first
-	* busy tick after returning from idle, we will update the busy stats.
-	*/
+	/*
+	 * We may be recently in ticked or tickless idle mode. At the first
+	 * busy tick after returning from idle, we will update the busy stats.
+	 */
 	set_cpu_sd_state_busy();
 	nohz_balance_exit_idle(cpu);
 
@@ -7213,7 +7250,7 @@ need_kick:
 	return 1;
 }
 #else
-static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) { }
+static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle, struct cpumask *mask) { }
 #endif
 
 /*
-- 
1.7.9.5

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