sched: Calculate energy consumption of sched_group

For energy-aware load-balancing decisions it is necessary to know the
energy consumption estimates of groups of cpus. This patch introduces a
basic function, sched_group_energy(), which estimates the energy
consumption of the cpus in the group and any resources shared by the
members of the group.

NOTE: The function has five levels of identation and breaks the 80
character limit. Refactoring is necessary.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9d82f4c47e3b8f3d400df69f46b8f3a9a3945c1e..a8f33eedbe8f418bb4b8a3b3609dee61f78a3742 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5994,6 +5994,7 @@ DEFINE_PER_CPU(struct sched_domain *, sd_numa);
 DEFINE_PER_CPU(struct sched_domain *, sd_busy);
 DEFINE_PER_CPU(struct sched_domain *, sd_asym);
 DEFINE_PER_CPU(struct sched_domain *, sd_ea);
+DEFINE_PER_CPU(struct sched_domain *, sd_scs);
 
 static void update_top_cache_domain(int cpu)
 {
@@ -6027,6 +6028,9 @@ static void update_top_cache_domain(int cpu)
                        break;
        }
        rcu_assign_pointer(per_cpu(sd_ea, cpu), ea_sd);
+
+       sd = highest_flag_domain(cpu, SD_SHARE_CAP_STATES);
+       rcu_assign_pointer(per_cpu(sd_scs, cpu), sd);
 }
 
 /*

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 318141042a3e67459663cc0bb36b1fe2be2cee58..49f7567c6b07457c0718b3a0bff7e93180a3c47f 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4701,6 +4701,162 @@ static inline bool energy_aware(void)
        return sched_feat(ENERGY_AWARE);
 }
 
+/*
+ * cpu_norm_util() returns the cpu util relative to a specific capacity,
+ * i.e. it's busy ratio, in the range [0..SCHED_LOAD_SCALE] which is useful for
+ * energy calculations. Using the scale-invariant util returned by
+ * cpu_util() and approximating scale-invariant util by:
+ *
+ *   util ~ (curr_freq/max_freq)*1024 * capacity_orig/1024 * running_time/time
+ *
+ * the normalized util can be found using the specific capacity.
+ *
+ *   capacity = capacity_orig * curr_freq/max_freq
+ *
+ *   norm_util = running_time/time ~ util/capacity
+ */
+static unsigned long cpu_norm_util(int cpu, unsigned long capacity)
+{
+       int util = cpu_util(cpu);
+
+       if (util >= capacity)
+               return SCHED_CAPACITY_SCALE;
+
+       return (util << SCHED_CAPACITY_SHIFT)/capacity;
+}
+
+static unsigned long group_max_util(struct sched_group *sg)
+{
+       int i;
+       unsigned long max_util = 0;
+
+       for_each_cpu(i, sched_group_cpus(sg))
+               max_util = max(max_util, cpu_util(i));
+
+       return max_util;
+}
+
+/*
+ * group_norm_util() returns the approximated group util relative to it's
+ * current capacity (busy ratio) in the range [0..SCHED_LOAD_SCALE] for use in
+ * energy calculations. Since task executions may or may not overlap in time in
+ * the group the true normalized util is between max(cpu_norm_util(i)) and
+ * sum(cpu_norm_util(i)) when iterating over all cpus in the group, i. The
+ * latter is used as the estimate as it leads to a more pessimistic energy
+ * estimate (more busy).
+ */
+static unsigned long group_norm_util(struct sched_group *sg, int cap_idx)
+{
+       int i;
+       unsigned long util_sum = 0;
+       unsigned long capacity = sg->sge->cap_states[cap_idx].cap;
+
+       for_each_cpu(i, sched_group_cpus(sg))
+               util_sum += cpu_norm_util(i, capacity);
+
+       if (util_sum > SCHED_CAPACITY_SCALE)
+               return SCHED_CAPACITY_SCALE;
+       return util_sum;
+}
+
+static int find_new_capacity(struct sched_group *sg,
+       const struct sched_group_energy const *sge)
+{
+       int idx;
+       unsigned long util = group_max_util(sg);
+
+       for (idx = 0; idx < sge->nr_cap_states; idx++) {
+               if (sge->cap_states[idx].cap >= util)
+                       return idx;
+       }
+
+       return idx;
+}
+
+/*
+ * sched_group_energy(): Computes the absolute energy consumption of cpus
+ * belonging to the sched_group including shared resources shared only by
+ * members of the group. Iterates over all cpus in the hierarchy below the
+ * sched_group starting from the bottom working it's way up before going to
+ * the next cpu until all cpus are covered at all levels. The current
+ * implementation is likely to gather the same util statistics multiple times.
+ * This can probably be done in a faster but more complex way.
+ * Note: sched_group_energy() may fail when racing with sched_domain updates.
+ */
+static int sched_group_energy(struct sched_group *sg_top)
+{
+       struct sched_domain *sd;
+       int cpu, total_energy = 0;
+       struct cpumask visit_cpus;
+       struct sched_group *sg;
+
+       WARN_ON(!sg_top->sge);
+
+       cpumask_copy(&visit_cpus, sched_group_cpus(sg_top));
+
+       while (!cpumask_empty(&visit_cpus)) {
+               struct sched_group *sg_shared_cap = NULL;
+
+               cpu = cpumask_first(&visit_cpus);
+
+               /*
+                * Is the group utilization affected by cpus outside this
+                * sched_group?
+                */
+               sd = rcu_dereference(per_cpu(sd_scs, cpu));
+
+               if (!sd)
+                       /*
+                        * We most probably raced with hotplug; returning a
+                        * wrong energy estimation is better than entering an
+                        * infinite loop.
+                        */
+                       return -EINVAL;
+
+               if (sd->parent)
+                       sg_shared_cap = sd->parent->groups;
+
+               for_each_domain(cpu, sd) {
+                       sg = sd->groups;
+
+                       /* Has this sched_domain already been visited? */
+                       if (sd->child && group_first_cpu(sg) != cpu)
+                               break;
+
+                       do {
+                               struct sched_group *sg_cap_util;
+                               unsigned long group_util;
+                               int sg_busy_energy, sg_idle_energy, cap_idx;
+
+                               if (sg_shared_cap && sg_shared_cap->group_weight >= sg->group_weight)
+                                       sg_cap_util = sg_shared_cap;
+                               else
+                                       sg_cap_util = sg;
+
+                               cap_idx = find_new_capacity(sg_cap_util, sg->sge);
+                               group_util = group_norm_util(sg, cap_idx);
+                               sg_busy_energy = (group_util * sg->sge->cap_states[cap_idx].power)
+                                                                               >> SCHED_CAPACITY_SHIFT;
+                               sg_idle_energy = ((SCHED_LOAD_SCALE-group_util) * sg->sge->idle_states[0].power)
+                                                                               >> SCHED_CAPACITY_SHIFT;
+
+                               total_energy += sg_busy_energy + sg_idle_energy;
+
+                               if (!sd->child)
+                                       cpumask_xor(&visit_cpus, &visit_cpus, sched_group_cpus(sg));
+
+                               if (cpumask_equal(sched_group_cpus(sg), sched_group_cpus(sg_top)))
+                                       goto next_cpu;
+
+                       } while (sg = sg->next, sg != sd->groups);
+               }
+next_cpu:
+               continue;
+       }
+
+       return total_energy;
+}
+
 /*
  * Detect M:N waker/wakee relationships via a switching-frequency heuristic.
  * A waker of many should wake a different task than the one last awakened

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index a77516a15ba019c955a81722956eda85cd6e636b..a618db2936d4ee95e40fea08802dce0d1b877178 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -840,6 +840,7 @@ DECLARE_PER_CPU(struct sched_domain *, sd_numa);
 DECLARE_PER_CPU(struct sched_domain *, sd_busy);
 DECLARE_PER_CPU(struct sched_domain *, sd_asym);
 DECLARE_PER_CPU(struct sched_domain *, sd_ea);
+DECLARE_PER_CPU(struct sched_domain *, sd_scs);
 
 struct sched_group_capacity {
        atomic_t ref;