[PATCH] sched: balance timers

Do CPU load averaging over a number of different intervals.  Allow each
interval to be chosen by sending a parameter to source_load and target_load.
0 is instantaneous, idx > 0 returns a decaying average with the most recent
sample weighted at 2^(idx-1).  To a maximum of 3 (could be easily increased).

So generally a higher number will result in more conservative balancing.

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 74 insertions, 64 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index f665de34ed82..b597b07e7911 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -206,7 +206,7 @@ struct runqueue {
          */
         unsigned long nr_running;
 #ifdef CONFIG_SMP
-        unsigned long cpu_load;
+        unsigned long cpu_load[3];
 #endif
         unsigned long long nr_switches;
 
@@ -886,23 +886,27 @@ void kick_process(task_t *p)
  * We want to under-estimate the load of migration sources, to
  * balance conservatively.
  */
-static inline unsigned long source_load(int cpu)
+static inline unsigned long source_load(int cpu, int type)
 {
         runqueue_t *rq = cpu_rq(cpu);
         unsigned long load_now = rq->nr_running * SCHED_LOAD_SCALE;
+        if (type == 0)
+                return load_now;
 
-        return min(rq->cpu_load, load_now);
+        return min(rq->cpu_load[type-1], load_now);
 }
 
 /*
  * Return a high guess at the load of a migration-target cpu
  */
-static inline unsigned long target_load(int cpu)
+static inline unsigned long target_load(int cpu, int type)
 {
         runqueue_t *rq = cpu_rq(cpu);
         unsigned long load_now = rq->nr_running * SCHED_LOAD_SCALE;
+        if (type == 0)
+                return load_now;
 
-        return max(rq->cpu_load, load_now);
+        return max(rq->cpu_load[type-1], load_now);
 }
 
 #endif
@@ -967,7 +971,7 @@ static int try_to_wake_up(task_t * p, unsigned int state, int sync)
         runqueue_t *rq;
 #ifdef CONFIG_SMP
         unsigned long load, this_load;
-        struct sched_domain *sd;
+        struct sched_domain *sd, *this_sd = NULL;
         int new_cpu;
 #endif
 
@@ -986,72 +990,64 @@ static int try_to_wake_up(task_t * p, unsigned int state, int sync)
         if (unlikely(task_running(rq, p)))
                 goto out_activate;
 
-#ifdef CONFIG_SCHEDSTATS
+        new_cpu = cpu;
+
         schedstat_inc(rq, ttwu_cnt);
         if (cpu == this_cpu) {
                 schedstat_inc(rq, ttwu_local);
-        } else {
-                for_each_domain(this_cpu, sd) {
-                        if (cpu_isset(cpu, sd->span)) {
-                                schedstat_inc(sd, ttwu_wake_remote);
-                                break;
-                        }
+                goto out_set_cpu;
+        }
+
+        for_each_domain(this_cpu, sd) {
+                if (cpu_isset(cpu, sd->span)) {
+                        schedstat_inc(sd, ttwu_wake_remote);
+                        this_sd = sd;
+                        break;
                 }
         }
-#endif
 
-        new_cpu = cpu;
-        if (cpu == this_cpu || unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
+        if (unlikely(!cpu_isset(this_cpu, p->cpus_allowed)))
                 goto out_set_cpu;
 
-        load = source_load(cpu);
-        this_load = target_load(this_cpu);
-
         /*
-         * If sync wakeup then subtract the (maximum possible) effect of
-         * the currently running task from the load of the current CPU:
+         * Check for affine wakeup and passive balancing possibilities.
          */
-        if (sync)
-                this_load -= SCHED_LOAD_SCALE;
-
-        /* Don't pull the task off an idle CPU to a busy one */
-        if (load < SCHED_LOAD_SCALE/2 && this_load > SCHED_LOAD_SCALE/2)
-                goto out_set_cpu;
+        if (this_sd) {
+                int idx = this_sd->wake_idx;
+                unsigned int imbalance;
 
-        new_cpu = this_cpu; /* Wake to this CPU if we can */
+                load = source_load(cpu, idx);
+                this_load = target_load(this_cpu, idx);
 
-        /*
-         * Scan domains for affine wakeup and passive balancing
-         * possibilities.
-         */
-        for_each_domain(this_cpu, sd) {
-                unsigned int imbalance;
                 /*
-                 * Start passive balancing when half the imbalance_pct
-                 * limit is reached.
+                 * If sync wakeup then subtract the (maximum possible) effect of
+                 * the currently running task from the load of the current CPU:
                  */
-                imbalance = sd->imbalance_pct + (sd->imbalance_pct - 100) / 2;
+                if (sync)
+                        this_load -= SCHED_LOAD_SCALE;
+
+                 /* Don't pull the task off an idle CPU to a busy one */
+                if (load < SCHED_LOAD_SCALE/2 && this_load > SCHED_LOAD_SCALE/2)
+                        goto out_set_cpu;
 
-                if ((sd->flags & SD_WAKE_AFFINE) &&
-                                !task_hot(p, rq->timestamp_last_tick, sd)) {
+                new_cpu = this_cpu; /* Wake to this CPU if we can */
+
+                if ((this_sd->flags & SD_WAKE_AFFINE) &&
+                        !task_hot(p, rq->timestamp_last_tick, this_sd)) {
                         /*
                          * This domain has SD_WAKE_AFFINE and p is cache cold
                          * in this domain.
                          */
-                        if (cpu_isset(cpu, sd->span)) {
-                                schedstat_inc(sd, ttwu_move_affine);
-                                goto out_set_cpu;
-                        }
-                } else if ((sd->flags & SD_WAKE_BALANCE) &&
+                        schedstat_inc(this_sd, ttwu_move_affine);
+                        goto out_set_cpu;
+                } else if ((this_sd->flags & SD_WAKE_BALANCE) &&
                                 imbalance*this_load <= 100*load) {
                         /*
                          * This domain has SD_WAKE_BALANCE and there is
                          * an imbalance.
                          */
-                        if (cpu_isset(cpu, sd->span)) {
-                                schedstat_inc(sd, ttwu_move_balance);
-                                goto out_set_cpu;
-                        }
+                        schedstat_inc(this_sd, ttwu_move_balance);
+                        goto out_set_cpu;
                 }
         }
 
@@ -1509,7 +1505,7 @@ static int find_idlest_cpu(struct task_struct *p, int this_cpu,
         cpus_and(mask, sd->span, p->cpus_allowed);
 
         for_each_cpu_mask(i, mask) {
-                load = target_load(i);
+                load = target_load(i, sd->wake_idx);
 
                 if (load < min_load) {
                         min_cpu = i;
@@ -1522,7 +1518,7 @@ static int find_idlest_cpu(struct task_struct *p, int this_cpu,
         }
 
         /* add +1 to account for the new task */
-        this_load = source_load(this_cpu) + SCHED_LOAD_SCALE;
+        this_load = source_load(this_cpu, sd->wake_idx) + SCHED_LOAD_SCALE;
 
         /*
          * Would with the addition of the new task to the
@@ -1767,8 +1763,15 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
 {
         struct sched_group *busiest = NULL, *this = NULL, *group = sd->groups;
         unsigned long max_load, avg_load, total_load, this_load, total_pwr;
+        int load_idx;
 
         max_load = this_load = total_load = total_pwr = 0;
+        if (idle == NOT_IDLE)
+                load_idx = sd->busy_idx;
+        else if (idle == NEWLY_IDLE)
+                load_idx = sd->newidle_idx;
+        else
+                load_idx = sd->idle_idx;
 
         do {
                 unsigned long load;
@@ -1783,9 +1786,9 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
                 for_each_cpu_mask(i, group->cpumask) {
                         /* Bias balancing toward cpus of our domain */
                         if (local_group)
-                                load = target_load(i);
+                                load = target_load(i, load_idx);
                         else
-                                load = source_load(i);
+                                load = source_load(i, load_idx);
 
                         avg_load += load;
                 }
@@ -1895,7 +1898,7 @@ static runqueue_t *find_busiest_queue(struct sched_group *group)
         int i;
 
         for_each_cpu_mask(i, group->cpumask) {
-                load = source_load(i);
+                load = source_load(i, 0);
 
                 if (load > max_load) {
                         max_load = load;
@@ -2150,18 +2153,23 @@ static void rebalance_tick(int this_cpu, runqueue_t *this_rq,
         unsigned long old_load, this_load;
         unsigned long j = jiffies + CPU_OFFSET(this_cpu);
         struct sched_domain *sd;
+        int i;
 
-        /* Update our load */
-        old_load = this_rq->cpu_load;
         this_load = this_rq->nr_running * SCHED_LOAD_SCALE;
-        /*
-         * Round up the averaging division if load is increasing. This
-         * prevents us from getting stuck on 9 if the load is 10, for
-         * example.
-         */
-        if (this_load > old_load)
-                old_load++;
-        this_rq->cpu_load = (old_load + this_load) / 2;
+        /* Update our load */
+        for (i = 0; i < 3; i++) {
+                unsigned long new_load = this_load;
+                int scale = 1 << i;
+                old_load = this_rq->cpu_load[i];
+                /*
+                 * Round up the averaging division if load is increasing. This
+                 * prevents us from getting stuck on 9 if the load is 10, for
+                 * example.
+                 */
+                if (new_load > old_load)
+                        new_load += scale-1;
+                this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) / scale;
+        }
 
         for_each_domain(this_cpu, sd) {
                 unsigned long interval;
@@ -4921,13 +4929,15 @@ void __init sched_init(void)
 
                 rq = cpu_rq(i);
                 spin_lock_init(&rq->lock);
+                rq->nr_running = 0;
                 rq->active = rq->arrays;
                 rq->expired = rq->arrays + 1;
                 rq->best_expired_prio = MAX_PRIO;
 
 #ifdef CONFIG_SMP
                 rq->sd = &sched_domain_dummy;
-                rq->cpu_load = 0;
+                for (j = 1; j < 3; j++)
+                        rq->cpu_load[j] = 0;
                 rq->active_balance = 0;
                 rq->push_cpu = 0;
                 rq->migration_thread = NULL;