2 files changed, 44 insertions, 11 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a3e5b1cd043..c731296e5e9 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -857,7 +857,7 @@ struct sched_group {
          * CPU power of this group, SCHED_LOAD_SCALE being max power for a
          * single CPU.
          */
-        unsigned int cpu_power;
+        unsigned int cpu_power, cpu_power_orig;
 
         /*
          * The CPUs this group covers.
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 6ee2e0af665..b9b3462483b 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2285,13 +2285,6 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
         unsigned long power = SCHED_LOAD_SCALE;
         struct sched_group *sdg = sd->groups;
 
-        if (sched_feat(ARCH_POWER))
-                power *= arch_scale_freq_power(sd, cpu);
-        else
-                power *= default_scale_freq_power(sd, cpu);
-
-        power >>= SCHED_LOAD_SHIFT;
-
         if ((sd->flags & SD_SHARE_CPUPOWER) && weight > 1) {
                 if (sched_feat(ARCH_POWER))
                         power *= arch_scale_smt_power(sd, cpu);
@@ -2301,6 +2294,15 @@ static void update_cpu_power(struct sched_domain *sd, int cpu)
                 power >>= SCHED_LOAD_SHIFT;
         }
 
+        sdg->cpu_power_orig = power;
+
+        if (sched_feat(ARCH_POWER))
+                power *= arch_scale_freq_power(sd, cpu);
+        else
+                power *= default_scale_freq_power(sd, cpu);
+
+        power >>= SCHED_LOAD_SHIFT;
+
         power *= scale_rt_power(cpu);
         power >>= SCHED_LOAD_SHIFT;
 
@@ -2333,6 +2335,31 @@ static void update_group_power(struct sched_domain *sd, int cpu)
         sdg->cpu_power = power;
 }
 
+/*
+ * Try and fix up capacity for tiny siblings, this is needed when
+ * things like SD_ASYM_PACKING need f_b_g to select another sibling
+ * which on its own isn't powerful enough.
+ *
+ * See update_sd_pick_busiest() and check_asym_packing().
+ */
+static inline int
+fix_small_capacity(struct sched_domain *sd, struct sched_group *group)
+{
+        /*
+         * Only siblings can have significantly less than SCHED_LOAD_SCALE
+         */
+        if (sd->level != SD_LV_SIBLING)
+                return 0;
+
+        /*
+         * If ~90% of the cpu_power is still there, we're good.
+         */
+        if (group->cpu_power * 32 < group->cpu_power_orig * 29)
+                return 1;
+
+        return 0;
+}
+
 /**
  * update_sg_lb_stats - Update sched_group's statistics for load balancing.
  * @sd: The sched_domain whose statistics are to be updated.
@@ -2426,6 +2453,8 @@ static inline void update_sg_lb_stats(struct sched_domain *sd,
 
         sgs->group_capacity =
                 DIV_ROUND_CLOSEST(group->cpu_power, SCHED_LOAD_SCALE);
+        if (!sgs->group_capacity)
+                sgs->group_capacity = fix_small_capacity(sd, group);
 }
 
 /**
@@ -2724,8 +2753,9 @@ ret:
  * find_busiest_queue - find the busiest runqueue among the cpus in group.
  */
 static struct rq *
-find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
-                   unsigned long imbalance, const struct cpumask *cpus)
+find_busiest_queue(struct sched_domain *sd, struct sched_group *group,
+                   enum cpu_idle_type idle, unsigned long imbalance,
+                   const struct cpumask *cpus)
 {
         struct rq *busiest = NULL, *rq;
         unsigned long max_load = 0;
@@ -2736,6 +2766,9 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
                 unsigned long capacity = DIV_ROUND_CLOSEST(power, SCHED_LOAD_SCALE);
                 unsigned long wl;
 
+                if (!capacity)
+                        capacity = fix_small_capacity(sd, group);
+
                 if (!cpumask_test_cpu(i, cpus))
                         continue;
 
@@ -2852,7 +2885,7 @@ redo:
                 goto out_balanced;
         }
 
-        busiest = find_busiest_queue(group, idle, imbalance, cpus);
+        busiest = find_busiest_queue(sd, group, idle, imbalance, cpus);
         if (!busiest) {
                 schedstat_inc(sd, lb_nobusyq[idle]);
                 goto out_balanced;