[RFC PATCH 8/9 v4] Implement Workload Consolidation in nohz_idle_balance

[Yuyang Du]

In periodic nohz idle balance, we skip kicking idle but non-consolidated CPUs.

Signed-off-by: Yuyang Du <yuyang...@intel.com>
---
 kernel/sched/fair.c |   55 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 45 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bf65fde..549f6e0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6983,10 +6983,45 @@ 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();
+
+               sd = per_cpu(sd_wc, this_cpu);
+               if (sd) {
+                       struct cpumask *nonshielded_cpus = 
__get_cpu_var(load_balance_mask);
+
+                       cpumask_copy(nonshielded_cpus, nohz.idle_cpus_mask);
+
+                       rcu_read_lock();
+                       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
+                       return ilb;
+       }
 
        return nr_cpu_ids;
 }
@@ -7217,7 +7252,7 @@ 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;
@@ -7227,7 +7262,7 @@ 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;
 
@@ -7280,10 +7315,10 @@ 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);
 
@@ -7326,7 +7361,7 @@ 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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