sched: Extend scheduler's asym packing

We generalize the scheduler's asym packing to provide an ordering
of the cpu beyond just the cpu number.  This allows the use of the
ASYM_PACKING scheduler machinery to move loads to preferred CPU in a
sched domain. The preference is defined with the cpu priority
given by arch_asym_cpu_priority(cpu).

We also record the most preferred cpu in a sched group when
we build the cpu's capacity for fast lookup of preferred cpu
during load balancing.

Co-developed-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-pm@vger.kernel.org
Cc: jolsa@redhat.com
Cc: rjw@rjwysocki.net
Cc: linux-acpi@vger.kernel.org
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: bp@suse.de
Link: http://lkml.kernel.org/r/0e73ae12737dfaafa46c07066cc7c5d3f1675e46.1479844244.git.tim.c.chen@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

4 files changed, 59 insertions, 17 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 19abba04ceca..fe9a499d5aa4 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1077,6 +1077,8 @@ static inline int cpu_numa_flags(void)
 }
 #endif
 
+extern int arch_asym_cpu_priority(int cpu);
+
 struct sched_domain_attr {
         int relax_domain_level;
 };
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index dc64bd71ed2b..393759bd526e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6303,7 +6303,22 @@ static void init_sched_groups_capacity(int cpu, struct sched_domain *sd)
         WARN_ON(!sg);
 
         do {
+                int cpu, max_cpu = -1;
+
                 sg->group_weight = cpumask_weight(sched_group_cpus(sg));
+
+                if (!(sd->flags & SD_ASYM_PACKING))
+                        goto next;
+
+                for_each_cpu(cpu, sched_group_cpus(sg)) {
+                        if (max_cpu < 0)
+                                max_cpu = cpu;
+                        else if (sched_asym_prefer(cpu, max_cpu))
+                                max_cpu = cpu;
+                }
+                sg->asym_prefer_cpu = max_cpu;
+
+next:
                 sg = sg->next;
         } while (sg != sd->groups);
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index aa475896782d..18d9e75f1f6e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -97,6 +97,16 @@ unsigned int normalized_sysctl_sched_wakeup_granularity	= 1000000UL;
 
 const_debug unsigned int sysctl_sched_migration_cost    = 500000UL;
 
+#ifdef CONFIG_SMP
+/*
+ * For asym packing, by default the lower numbered cpu has higher priority.
+ */
+int __weak arch_asym_cpu_priority(int cpu)
+{
+        return -cpu;
+}
+#endif
+
 #ifdef CONFIG_CFS_BANDWIDTH
 /*
  * Amount of runtime to allocate from global (tg) to local (per-cfs_rq) pool
@@ -7388,16 +7398,18 @@ asym_packing:
         if (env->idle == CPU_NOT_IDLE)
                 return true;
         /*
-         * ASYM_PACKING needs to move all the work to the lowest
-         * numbered CPUs in the group, therefore mark all groups
-         * higher than ourself as busy.
+         * ASYM_PACKING needs to move all the work to the highest
+         * prority CPUs in the group, therefore mark all groups
+         * of lower priority than ourself as busy.
          */
-        if (sgs->sum_nr_running && env->dst_cpu < group_first_cpu(sg)) {
+        if (sgs->sum_nr_running &&
+            sched_asym_prefer(env->dst_cpu, sg->asym_prefer_cpu)) {
                 if (!sds->busiest)
                         return true;
 
-                /* Prefer to move from highest possible cpu's work */
-                if (group_first_cpu(sds->busiest) < group_first_cpu(sg))
+                /* Prefer to move from lowest priority cpu's work */
+                if (sched_asym_prefer(sds->busiest->asym_prefer_cpu,
+                                      sg->asym_prefer_cpu))
                         return true;
         }
 
@@ -7549,8 +7561,8 @@ static int check_asym_packing(struct lb_env *env, struct sd_lb_stats *sds)
         if (!sds->busiest)
                 return 0;
 
-        busiest_cpu = group_first_cpu(sds->busiest);
-        if (env->dst_cpu > busiest_cpu)
+        busiest_cpu = sds->busiest->asym_prefer_cpu;
+        if (sched_asym_prefer(busiest_cpu, env->dst_cpu))
                 return 0;
 
         env->imbalance = DIV_ROUND_CLOSEST(
@@ -7888,10 +7900,11 @@ static int need_active_balance(struct lb_env *env)
 
                 /*
                  * ASYM_PACKING needs to force migrate tasks from busy but
-                 * higher numbered CPUs in order to pack all tasks in the
-                 * lowest numbered CPUs.
+                 * lower priority CPUs in order to pack all tasks in the
+                 * highest priority CPUs.
                  */
-                if ((sd->flags & SD_ASYM_PACKING) && env->src_cpu > env->dst_cpu)
+                if ((sd->flags & SD_ASYM_PACKING) &&
+                    sched_asym_prefer(env->dst_cpu, env->src_cpu))
                         return 1;
         }
 
@@ -8740,7 +8753,7 @@ static inline bool nohz_kick_needed(struct rq *rq)
         unsigned long now = jiffies;
         struct sched_domain_shared *sds;
         struct sched_domain *sd;
-        int nr_busy, cpu = rq->cpu;
+        int nr_busy, i, cpu = rq->cpu;
         bool kick = false;
 
         if (unlikely(rq->idle_balance))
@@ -8791,12 +8804,18 @@ static inline bool nohz_kick_needed(struct rq *rq)
         }
 
         sd = rcu_dereference(per_cpu(sd_asym, cpu));
-        if (sd && (cpumask_first_and(nohz.idle_cpus_mask,
-                                  sched_domain_span(sd)) < cpu)) {
-                kick = true;
-                goto unlock;
-        }
+        if (sd) {
+                for_each_cpu(i, sched_domain_span(sd)) {
+                        if (i == cpu ||
+                            !cpumask_test_cpu(i, nohz.idle_cpus_mask))
+                                continue;
 
+                        if (sched_asym_prefer(i, cpu)) {
+                                kick = true;
+                                goto unlock;
+                        }
+                }
+        }
 unlock:
         rcu_read_unlock();
         return kick;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index d7e39317d688..7b34c7826ca5 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -540,6 +540,11 @@ struct dl_rq {
 
 #ifdef CONFIG_SMP
 
+static inline bool sched_asym_prefer(int a, int b)
+{
+        return arch_asym_cpu_priority(a) > arch_asym_cpu_priority(b);
+}
+
 /*
  * We add the notion of a root-domain which will be used to define per-domain
  * variables. Each exclusive cpuset essentially defines an island domain by
@@ -908,6 +913,7 @@ struct sched_group {
 
         unsigned int group_weight;
         struct sched_group_capacity *sgc;
+        int asym_prefer_cpu;            /* cpu of highest priority in group */
 
         /*
          * The CPUs this group covers.