sched: Merge select_task_rq_fair() and sched_balance_self()

The problem with wake_idle() is that is doesn't respect things like
cpu_power, which means it doesn't deal well with SMT nor the recent
RT interaction.

To cure this, it needs to do what sched_balance_self() does, which
leads to the possibility of merging select_task_rq_fair() and
sched_balance_self().

Modify sched_balance_self() to:

  - update_shares() when walking up the domain tree,
    (it only called it for the top domain, but it should
     have done this anyway), which allows us to remove
    this ugly bit from try_to_wake_up().

  - do wake_affine() on the smallest domain that contains
    both this (the waking) and the prev (the wakee) cpu for
    WAKE invocations.

Then use the top-down balance steps it had to replace wake_idle().

This leads to the dissapearance of SD_WAKE_BALANCE and
SD_WAKE_IDLE_FAR, with SD_WAKE_IDLE replaced with SD_BALANCE_WAKE.

SD_WAKE_AFFINE needs SD_BALANCE_WAKE to be effective.

Touch all topology bits to replace the old with new SD flags --
platforms might need re-tuning, enabling SD_BALANCE_WAKE
conditionally on a NUMA distance seems like a good additional
feature, magny-core and small nehalem systems would want this
enabled, systems with slow interconnects would not.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 63 insertions, 170 deletions

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index f2eb5b934715..09d19f77eb3a 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1062,83 +1062,6 @@ static void yield_task_fair(struct rq *rq)
         se->vruntime = rightmost->vruntime + 1;
 }
 
-/*
- * wake_idle() will wake a task on an idle cpu if task->cpu is
- * not idle and an idle cpu is available.  The span of cpus to
- * search starts with cpus closest then further out as needed,
- * so we always favor a closer, idle cpu.
- * Domains may include CPUs that are not usable for migration,
- * hence we need to mask them out (rq->rd->online)
- *
- * Returns the CPU we should wake onto.
- */
-#if defined(ARCH_HAS_SCHED_WAKE_IDLE)
-
-#define cpu_rd_active(cpu, rq) cpumask_test_cpu(cpu, rq->rd->online)
-
-static int wake_idle(int cpu, struct task_struct *p)
-{
-        struct sched_domain *sd;
-        int i;
-        unsigned int chosen_wakeup_cpu;
-        int this_cpu;
-        struct rq *task_rq = task_rq(p);
-
-        /*
-         * At POWERSAVINGS_BALANCE_WAKEUP level, if both this_cpu and prev_cpu
-         * are idle and this is not a kernel thread and this task's affinity
-         * allows it to be moved to preferred cpu, then just move!
-         */
-
-        this_cpu = smp_processor_id();
-        chosen_wakeup_cpu =
-                cpu_rq(this_cpu)->rd->sched_mc_preferred_wakeup_cpu;
-
-        if (sched_mc_power_savings >= POWERSAVINGS_BALANCE_WAKEUP &&
-                idle_cpu(cpu) && idle_cpu(this_cpu) &&
-                p->mm && !(p->flags & PF_KTHREAD) &&
-                cpu_isset(chosen_wakeup_cpu, p->cpus_allowed))
-                return chosen_wakeup_cpu;
-
-        /*
-         * If it is idle, then it is the best cpu to run this task.
-         *
-         * This cpu is also the best, if it has more than one task already.
-         * Siblings must be also busy(in most cases) as they didn't already
-         * pickup the extra load from this cpu and hence we need not check
-         * sibling runqueue info. This will avoid the checks and cache miss
-         * penalities associated with that.
-         */
-        if (idle_cpu(cpu) || cpu_rq(cpu)->cfs.nr_running > 1)
-                return cpu;
-
-        for_each_domain(cpu, sd) {
-                if ((sd->flags & SD_WAKE_IDLE)
-                    || ((sd->flags & SD_WAKE_IDLE_FAR)
-                        && !task_hot(p, task_rq->clock, sd))) {
-                        for_each_cpu_and(i, sched_domain_span(sd),
-                                         &p->cpus_allowed) {
-                                if (cpu_rd_active(i, task_rq) && idle_cpu(i)) {
-                                        if (i != task_cpu(p)) {
-                                                schedstat_inc(p,
-                                                       se.nr_wakeups_idle);
-                                        }
-                                        return i;
-                                }
-                        }
-                } else {
-                        break;
-                }
-        }
-        return cpu;
-}
-#else /* !ARCH_HAS_SCHED_WAKE_IDLE*/
-static inline int wake_idle(int cpu, struct task_struct *p)
-{
-        return cpu;
-}
-#endif
-
 #ifdef CONFIG_SMP
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
@@ -1225,21 +1148,22 @@ static inline unsigned long effective_load(struct task_group *tg, int cpu,
 
 #endif
 
-static int
-wake_affine(struct sched_domain *this_sd, struct rq *this_rq,
-            struct task_struct *p, int prev_cpu, int this_cpu, int sync,
-            int idx, unsigned long load, unsigned long this_load,
-            unsigned int imbalance)
+static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
 {
-        struct task_struct *curr = this_rq->curr;
-        struct task_group *tg;
-        unsigned long tl = this_load;
+        struct task_struct *curr = current;
+        unsigned long this_load, load;
+        int idx, this_cpu, prev_cpu;
         unsigned long tl_per_task;
+        unsigned int imbalance;
+        struct task_group *tg;
         unsigned long weight;
         int balanced;
 
-        if (!(this_sd->flags & SD_WAKE_AFFINE) || !sched_feat(AFFINE_WAKEUPS))
-                return 0;
+        idx       = sd->wake_idx;
+        this_cpu  = smp_processor_id();
+        prev_cpu  = task_cpu(p);
+        load      = source_load(prev_cpu, idx);
+        this_load = target_load(this_cpu, idx);
 
         if (sync && (curr->se.avg_overlap > sysctl_sched_migration_cost ||
                         p->se.avg_overlap > sysctl_sched_migration_cost))
@@ -1254,24 +1178,26 @@ wake_affine(struct sched_domain *this_sd, struct rq *this_rq,
                 tg = task_group(current);
                 weight = current->se.load.weight;
 
-                tl += effective_load(tg, this_cpu, -weight, -weight);
+                this_load += effective_load(tg, this_cpu, -weight, -weight);
                 load += effective_load(tg, prev_cpu, 0, -weight);
         }
 
         tg = task_group(p);
         weight = p->se.load.weight;
 
+        imbalance = 100 + (sd->imbalance_pct - 100) / 2;
+
         /*
          * In low-load situations, where prev_cpu is idle and this_cpu is idle
-         * due to the sync cause above having dropped tl to 0, we'll always have
-         * an imbalance, but there's really nothing you can do about that, so
-         * that's good too.
+         * due to the sync cause above having dropped this_load to 0, we'll
+         * always have an imbalance, but there's really nothing you can do
+         * about that, so that's good too.
          *
          * Otherwise check if either cpus are near enough in load to allow this
          * task to be woken on this_cpu.
          */
-        balanced = !tl ||
-                100*(tl + effective_load(tg, this_cpu, weight, weight)) <=
+        balanced = !this_load ||
+                100*(this_load + effective_load(tg, this_cpu, weight, weight)) <=
                 imbalance*(load + effective_load(tg, prev_cpu, 0, weight));
 
         /*
@@ -1285,14 +1211,15 @@ wake_affine(struct sched_domain *this_sd, struct rq *this_rq,
         schedstat_inc(p, se.nr_wakeups_affine_attempts);
         tl_per_task = cpu_avg_load_per_task(this_cpu);
 
-        if (balanced || (tl <= load && tl + target_load(prev_cpu, idx) <=
-                        tl_per_task)) {
+        if (balanced ||
+            (this_load <= load &&
+             this_load + target_load(prev_cpu, idx) <= tl_per_task)) {
                 /*
                  * This domain has SD_WAKE_AFFINE and
                  * p is cache cold in this domain, and
                  * there is no bad imbalance.
                  */
-                schedstat_inc(this_sd, ttwu_move_affine);
+                schedstat_inc(sd, ttwu_move_affine);
                 schedstat_inc(p, se.nr_wakeups_affine);
 
                 return 1;
@@ -1300,72 +1227,6 @@ wake_affine(struct sched_domain *this_sd, struct rq *this_rq,
         return 0;
 }
 
-static int sched_balance_self(int cpu, int flag);
-
-static int select_task_rq_fair(struct task_struct *p, int flag, int sync)
-{
-        struct sched_domain *sd, *this_sd = NULL;
-        int prev_cpu, this_cpu, new_cpu;
-        unsigned long load, this_load;
-        struct rq *this_rq;
-        unsigned int imbalance;
-        int idx;
-
-        prev_cpu        = task_cpu(p);
-        this_cpu        = smp_processor_id();
-        this_rq         = cpu_rq(this_cpu);
-        new_cpu         = prev_cpu;
-
-        if (flag != SD_BALANCE_WAKE)
-                return sched_balance_self(this_cpu, flag);
-
-        /*
-         * 'this_sd' is the first domain that both
-         * this_cpu and prev_cpu are present in:
-         */
-        for_each_domain(this_cpu, sd) {
-                if (cpumask_test_cpu(prev_cpu, sched_domain_span(sd))) {
-                        this_sd = sd;
-                        break;
-                }
-        }
-
-        if (unlikely(!cpumask_test_cpu(this_cpu, &p->cpus_allowed)))
-                goto out;
-
-        /*
-         * Check for affine wakeup and passive balancing possibilities.
-         */
-        if (!this_sd)
-                goto out;
-
-        idx = this_sd->wake_idx;
-
-        imbalance = 100 + (this_sd->imbalance_pct - 100) / 2;
-
-        load = source_load(prev_cpu, idx);
-        this_load = target_load(this_cpu, idx);
-
-        if (wake_affine(this_sd, this_rq, p, prev_cpu, this_cpu, sync, idx,
-                                     load, this_load, imbalance))
-                return this_cpu;
-
-        /*
-         * Start passive balancing when half the imbalance_pct
-         * limit is reached.
-         */
-        if (this_sd->flags & SD_WAKE_BALANCE) {
-                if (imbalance*this_load <= 100*load) {
-                        schedstat_inc(this_sd, ttwu_move_balance);
-                        schedstat_inc(p, se.nr_wakeups_passive);
-                        return this_cpu;
-                }
-        }
-
-out:
-        return wake_idle(new_cpu, p);
-}
-
 /*
  * find_idlest_group finds and returns the least busy CPU group within the
  * domain.
@@ -1455,10 +1316,20 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
  *
  * preempt must be disabled.
  */
-static int sched_balance_self(int cpu, int flag)
+static int select_task_rq_fair(struct task_struct *p, int flag, int sync)
 {
         struct task_struct *t = current;
         struct sched_domain *tmp, *sd = NULL;
+        int cpu = smp_processor_id();
+        int prev_cpu = task_cpu(p);
+        int new_cpu = cpu;
+        int want_affine = 0;
+
+        if (flag & SD_BALANCE_WAKE) {
+                if (sched_feat(AFFINE_WAKEUPS))
+                        want_affine = 1;
+                new_cpu = prev_cpu;
+        }
 
         for_each_domain(cpu, tmp) {
                 /*
@@ -1466,16 +1337,38 @@ static int sched_balance_self(int cpu, int flag)
                  */
                 if (tmp->flags & SD_POWERSAVINGS_BALANCE)
                         break;
-                if (tmp->flags & flag)
-                        sd = tmp;
-        }
 
-        if (sd)
-                update_shares(sd);
+                switch (flag) {
+                case SD_BALANCE_WAKE:
+                        if (!sched_feat(LB_WAKEUP_UPDATE))
+                                break;
+                case SD_BALANCE_FORK:
+                case SD_BALANCE_EXEC:
+                        if (root_task_group_empty())
+                                break;
+                        update_shares(tmp);
+                default:
+                        break;
+                }
+
+                if (want_affine && (tmp->flags & SD_WAKE_AFFINE) &&
+                    cpumask_test_cpu(prev_cpu, sched_domain_span(tmp))) {
+
+                        if (wake_affine(tmp, p, sync))
+                                return cpu;
+
+                        want_affine = 0;
+                }
+
+                if (!(tmp->flags & flag))
+                        continue;
+
+                sd = tmp;
+        }
 
         while (sd) {
                 struct sched_group *group;
-                int new_cpu, weight;
+                int weight;
 
                 if (!(sd->flags & flag)) {
                         sd = sd->child;
@@ -1508,7 +1401,7 @@ static int sched_balance_self(int cpu, int flag)
                 /* while loop will break here if sd == NULL */
         }
 
-        return cpu;
+        return new_cpu;
 }
 #endif /* CONFIG_SMP */