[PATCH] sched: mc/smt power savings sched policy

sysfs entries 'sched_mc_power_savings' and 'sched_smt_power_savings' in
/sys/devices/system/cpu/ control the MC/SMT power savings policy for the
scheduler.

Based on the values (1-enable, 0-disable) for these controls, sched groups
cpu power will be determined for different domains.  When power savings
policy is enabled and under light load conditions, scheduler will minimize
the physical packages/cpu cores carrying the load and thus conserving
power(with a perf impact based on the workload characteristics...  see OLS
2005 CMP kernel scheduler paper for more details..)

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Con Kolivas <kernel@kolivas.org>
Cc: "Chen, Kenneth W" <kenneth.w.chen@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 215 insertions, 25 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 122b75584a13..54fa282657cc 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1162,6 +1162,11 @@ static int sched_balance_self(int cpu, int flag)
         struct sched_domain *tmp, *sd = NULL;
 
         for_each_domain(cpu, tmp) {
+                /*
+                 * If power savings logic is enabled for a domain, stop there.
+                 */
+                if (tmp->flags & SD_POWERSAVINGS_BALANCE)
+                        break;
                 if (tmp->flags & flag)
                         sd = tmp;
         }
@@ -2082,6 +2087,12 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
         unsigned long busiest_load_per_task, busiest_nr_running;
         unsigned long this_load_per_task, this_nr_running;
         int load_idx;
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+        int power_savings_balance = 1;
+        unsigned long leader_nr_running = 0, min_load_per_task = 0;
+        unsigned long min_nr_running = ULONG_MAX;
+        struct sched_group *group_min = NULL, *group_leader = NULL;
+#endif
 
         max_load = this_load = total_load = total_pwr = 0;
         busiest_load_per_task = busiest_nr_running = 0;
@@ -2094,7 +2105,7 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
                 load_idx = sd->idle_idx;
 
         do {
-                unsigned long load;
+                unsigned long load, group_capacity;
                 int local_group;
                 int i;
                 unsigned long sum_nr_running, sum_weighted_load;
@@ -2127,18 +2138,76 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
                 /* Adjust by relative CPU power of the group */
                 avg_load = (avg_load * SCHED_LOAD_SCALE) / group->cpu_power;
 
+                group_capacity = group->cpu_power / SCHED_LOAD_SCALE;
+
                 if (local_group) {
                         this_load = avg_load;
                         this = group;
                         this_nr_running = sum_nr_running;
                         this_load_per_task = sum_weighted_load;
                 } else if (avg_load > max_load &&
-                           sum_nr_running > group->cpu_power / SCHED_LOAD_SCALE) {
+                           sum_nr_running > group_capacity) {
                         max_load = avg_load;
                         busiest = group;
                         busiest_nr_running = sum_nr_running;
                         busiest_load_per_task = sum_weighted_load;
                 }
+
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+                /*
+                 * Busy processors will not participate in power savings
+                 * balance.
+                 */
+                if (idle == NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+                        goto group_next;
+
+                /*
+                 * If the local group is idle or completely loaded
+                 * no need to do power savings balance at this domain
+                 */
+                if (local_group && (this_nr_running >= group_capacity ||
+                                    !this_nr_running))
+                        power_savings_balance = 0;
+
+                /*
+                 * If a group is already running at full capacity or idle,
+                 * don't include that group in power savings calculations
+                 */
+                if (!power_savings_balance || sum_nr_running >= group_capacity
+                    || !sum_nr_running)
+                        goto group_next;
+
+                /*
+                 * Calculate the group which has the least non-idle load.
+                 * This is the group from where we need to pick up the load
+                 * for saving power
+                 */
+                if ((sum_nr_running < min_nr_running) ||
+                    (sum_nr_running == min_nr_running &&
+                     first_cpu(group->cpumask) <
+                     first_cpu(group_min->cpumask))) {
+                        group_min = group;
+                        min_nr_running = sum_nr_running;
+                        min_load_per_task = sum_weighted_load /
+                                                sum_nr_running;
+                }
+
+                /*
+                 * Calculate the group which is almost near its
+                 * capacity but still has some space to pick up some load
+                 * from other group and save more power
+                 */
+                if (sum_nr_running <= group_capacity - 1)
+                        if (sum_nr_running > leader_nr_running ||
+                            (sum_nr_running == leader_nr_running &&
+                             first_cpu(group->cpumask) >
+                              first_cpu(group_leader->cpumask))) {
+                                group_leader = group;
+                                leader_nr_running = sum_nr_running;
+                        }
+
+group_next:
+#endif
                 group = group->next;
         } while (group != sd->groups);
 
@@ -2247,7 +2316,16 @@ small_imbalance:
         return busiest;
 
 out_balanced:
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+        if (idle == NOT_IDLE || !(sd->flags & SD_POWERSAVINGS_BALANCE))
+                goto ret;
 
+        if (this == group_leader && group_leader != group_min) {
+                *imbalance = min_load_per_task;
+                return group_min;
+        }
+ret:
+#endif
         *imbalance = 0;
         return NULL;
 }
@@ -2300,7 +2378,8 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
         int active_balance = 0;
         int sd_idle = 0;
 
-        if (idle != NOT_IDLE && sd->flags & SD_SHARE_CPUPOWER)
+        if (idle != NOT_IDLE && sd->flags & SD_SHARE_CPUPOWER &&
+            !sched_smt_power_savings)
                 sd_idle = 1;
 
         schedstat_inc(sd, lb_cnt[idle]);
@@ -2389,7 +2468,8 @@ static int load_balance(int this_cpu, runqueue_t *this_rq,
                         sd->balance_interval *= 2;
         }
 
-        if (!nr_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+        if (!nr_moved && !sd_idle && sd->flags & SD_SHARE_CPUPOWER &&
+            !sched_smt_power_savings)
                 return -1;
         return nr_moved;
 
@@ -2404,7 +2484,7 @@ out_one_pinned:
                         (sd->balance_interval < sd->max_interval))
                 sd->balance_interval *= 2;
 
-        if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+        if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER && !sched_smt_power_savings)
                 return -1;
         return 0;
 }
@@ -2425,7 +2505,7 @@ static int load_balance_newidle(int this_cpu, runqueue_t *this_rq,
         int nr_moved = 0;
         int sd_idle = 0;
 
-        if (sd->flags & SD_SHARE_CPUPOWER)
+        if (sd->flags & SD_SHARE_CPUPOWER && !sched_smt_power_savings)
                 sd_idle = 1;
 
         schedstat_inc(sd, lb_cnt[NEWLY_IDLE]);
@@ -2466,7 +2546,7 @@ static int load_balance_newidle(int this_cpu, runqueue_t *this_rq,
 
 out_balanced:
         schedstat_inc(sd, lb_balanced[NEWLY_IDLE]);
-        if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER)
+        if (!sd_idle && sd->flags & SD_SHARE_CPUPOWER && !sched_smt_power_savings)
                 return -1;
         sd->nr_balance_failed = 0;
         return 0;
@@ -5732,6 +5812,7 @@ static cpumask_t sched_domain_node_span(int node)
 }
 #endif
 
+int sched_smt_power_savings = 0, sched_mc_power_savings = 0;
 /*
  * At the moment, CONFIG_SCHED_SMT is never defined, but leave it in so we
  * can switch it on easily if needed.
@@ -6113,37 +6194,72 @@ static int build_sched_domains(const cpumask_t *cpu_map)
 #endif
 
         /* Calculate CPU power for physical packages and nodes */
+#ifdef CONFIG_SCHED_SMT
         for_each_cpu_mask(i, *cpu_map) {
-                int power;
                 struct sched_domain *sd;
-#ifdef CONFIG_SCHED_SMT
                 sd = &per_cpu(cpu_domains, i);
-                power = SCHED_LOAD_SCALE;
-                sd->groups->cpu_power = power;
+                sd->groups->cpu_power = SCHED_LOAD_SCALE;
+        }
 #endif
 #ifdef CONFIG_SCHED_MC
+        for_each_cpu_mask(i, *cpu_map) {
+                int power;
+                struct sched_domain *sd;
                 sd = &per_cpu(core_domains, i);
-                power = SCHED_LOAD_SCALE + (cpus_weight(sd->groups->cpumask)-1)
+                if (sched_smt_power_savings)
+                        power = SCHED_LOAD_SCALE * cpus_weight(sd->groups->cpumask);
+                else
+                        power = SCHED_LOAD_SCALE + (cpus_weight(sd->groups->cpumask)-1)
                                             * SCHED_LOAD_SCALE / 10;
                 sd->groups->cpu_power = power;
+        }
+#endif
 
+        for_each_cpu_mask(i, *cpu_map) {
+                struct sched_domain *sd;
+#ifdef CONFIG_SCHED_MC
                 sd = &per_cpu(phys_domains, i);
+                if (i != first_cpu(sd->groups->cpumask))
+                        continue;
 
-                /*
-                 * This has to be < 2 * SCHED_LOAD_SCALE
-                 * Lets keep it SCHED_LOAD_SCALE, so that
-                 * while calculating NUMA group's cpu_power
-                 * we can simply do
-                 *  numa_group->cpu_power += phys_group->cpu_power;
-                 *
-                 * See "only add power once for each physical pkg"
-                 * comment below
-                 */
-                sd->groups->cpu_power = SCHED_LOAD_SCALE;
+                sd->groups->cpu_power = 0;
+                if (sched_mc_power_savings || sched_smt_power_savings) {
+                        int j;
+
+                        for_each_cpu_mask(j, sd->groups->cpumask) {
+                                struct sched_domain *sd1;
+                                sd1 = &per_cpu(core_domains, j);
+                                /*
+                                 * for each core we will add once
+                                 * to the group in physical domain
+                                 */
+                                if (j != first_cpu(sd1->groups->cpumask))
+                                        continue;
+
+                                if (sched_smt_power_savings)
+                                        sd->groups->cpu_power += sd1->groups->cpu_power;
+                                else
+                                        sd->groups->cpu_power += SCHED_LOAD_SCALE;
+                        }
+                } else
+                        /*
+                         * This has to be < 2 * SCHED_LOAD_SCALE
+                         * Lets keep it SCHED_LOAD_SCALE, so that
+                         * while calculating NUMA group's cpu_power
+                         * we can simply do
+                         *  numa_group->cpu_power += phys_group->cpu_power;
+                         *
+                         * See "only add power once for each physical pkg"
+                         * comment below
+                         */
+                        sd->groups->cpu_power = SCHED_LOAD_SCALE;
 #else
+                int power;
                 sd = &per_cpu(phys_domains, i);
-                power = SCHED_LOAD_SCALE + SCHED_LOAD_SCALE *
-                                (cpus_weight(sd->groups->cpumask)-1) / 10;
+                if (sched_smt_power_savings)
+                        power = SCHED_LOAD_SCALE * cpus_weight(sd->groups->cpumask);
+                else
+                        power = SCHED_LOAD_SCALE;
                 sd->groups->cpu_power = power;
 #endif
         }
@@ -6244,6 +6360,80 @@ int partition_sched_domains(cpumask_t *partition1, cpumask_t *partition2)
         return err;
 }
 
+#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
+int arch_reinit_sched_domains(void)
+{
+        int err;
+
+        lock_cpu_hotplug();
+        detach_destroy_domains(&cpu_online_map);
+        err = arch_init_sched_domains(&cpu_online_map);
+        unlock_cpu_hotplug();
+
+        return err;
+}
+
+static ssize_t sched_power_savings_store(const char *buf, size_t count, int smt)
+{
+        int ret;
+
+        if (buf[0] != '0' && buf[0] != '1')
+                return -EINVAL;
+
+        if (smt)
+                sched_smt_power_savings = (buf[0] == '1');
+        else
+                sched_mc_power_savings = (buf[0] == '1');
+
+        ret = arch_reinit_sched_domains();
+
+        return ret ? ret : count;
+}
+
+int sched_create_sysfs_power_savings_entries(struct sysdev_class *cls)
+{
+        int err = 0;
+#ifdef CONFIG_SCHED_SMT
+        if (smt_capable())
+                err = sysfs_create_file(&cls->kset.kobj,
+                                        &attr_sched_smt_power_savings.attr);
+#endif
+#ifdef CONFIG_SCHED_MC
+        if (!err && mc_capable())
+                err = sysfs_create_file(&cls->kset.kobj,
+                                        &attr_sched_mc_power_savings.attr);
+#endif
+        return err;
+}
+#endif
+
+#ifdef CONFIG_SCHED_MC
+static ssize_t sched_mc_power_savings_show(struct sys_device *dev, char *page)
+{
+        return sprintf(page, "%u\n", sched_mc_power_savings);
+}
+static ssize_t sched_mc_power_savings_store(struct sys_device *dev, const char *buf, size_t count)
+{
+        return sched_power_savings_store(buf, count, 0);
+}
+SYSDEV_ATTR(sched_mc_power_savings, 0644, sched_mc_power_savings_show,
+            sched_mc_power_savings_store);
+#endif
+
+#ifdef CONFIG_SCHED_SMT
+static ssize_t sched_smt_power_savings_show(struct sys_device *dev, char *page)
+{
+        return sprintf(page, "%u\n", sched_smt_power_savings);
+}
+static ssize_t sched_smt_power_savings_store(struct sys_device *dev, const char *buf, size_t count)
+{
+        return sched_power_savings_store(buf, count, 1);
+}
+SYSDEV_ATTR(sched_smt_power_savings, 0644, sched_smt_power_savings_show,
+            sched_smt_power_savings_store);
+#endif
+
+
 #ifdef CONFIG_HOTPLUG_CPU
 /*
  * Force a reinitialization of the sched domains hierarchy.  The domains