[PATCH] sched: consolidate sbe sbf

Consolidate balance-on-exec with balance-on-fork.  This is made easy by the
sched-domains RCU patches.

As well as the general goodness of code reduction, this allows the runqueues
to be unlocked during balance-on-fork.

schedstats is a problem.  Maybe just have balance-on-event instead of
distinguishing fork and exec?

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 80 insertions, 115 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index a28d11e10877..2c7806873bfd 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1003,9 +1003,6 @@ static task_t *copy_process(unsigned long clone_flags,
         p->pdeath_signal = 0;
         p->exit_state = 0;
 
-        /* Perform scheduler related setup */
-        sched_fork(p);
-
         /*
          * Ok, make it visible to the rest of the system.
          * We dont wake it up yet.
@@ -1014,18 +1011,24 @@ static task_t *copy_process(unsigned long clone_flags,
         INIT_LIST_HEAD(&p->ptrace_children);
         INIT_LIST_HEAD(&p->ptrace_list);
 
+        /* Perform scheduler related setup. Assign this task to a CPU. */
+        sched_fork(p, clone_flags);
+
         /* Need tasklist lock for parent etc handling! */
         write_lock_irq(&tasklist_lock);
 
         /*
-         * The task hasn't been attached yet, so cpus_allowed mask cannot
-         * have changed. The cpus_allowed mask of the parent may have
-         * changed after it was copied first time, and it may then move to
-         * another CPU - so we re-copy it here and set the child's CPU to
-         * the parent's CPU. This avoids alot of nasty races.
+         * The task hasn't been attached yet, so its cpus_allowed mask will
+         * not be changed, nor will its assigned CPU.
+         *
+         * The cpus_allowed mask of the parent may have changed after it was
+         * copied first time - so re-copy it here, then check the child's CPU
+         * to ensure it is on a valid CPU (and if not, just force it back to
+         * parent's CPU). This avoids alot of nasty races.
          */
         p->cpus_allowed = current->cpus_allowed;
-        set_task_cpu(p, smp_processor_id());
+        if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed)))
+                set_task_cpu(p, smp_processor_id());
 
         /*
          * Check for pending SIGKILL! The new thread should not be allowed
diff --git a/kernel/sched.c b/kernel/sched.c
index 54ce787b6207..579da278e72f 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1021,8 +1021,59 @@ static int find_idlest_cpu(struct sched_group *group, int this_cpu)
         return idlest;
 }
 
+/*
+ * sched_balance_self: balance the current task (running on cpu) in domains
+ * that have the 'flag' flag set. In practice, this is SD_BALANCE_FORK and
+ * SD_BALANCE_EXEC.
+ *
+ * Balance, ie. select the least loaded group.
+ *
+ * Returns the target CPU number, or the same CPU if no balancing is needed.
+ *
+ * preempt must be disabled.
+ */
+static int sched_balance_self(int cpu, int flag)
+{
+        struct task_struct *t = current;
+        struct sched_domain *tmp, *sd = NULL;
 
-#endif
+        for_each_domain(cpu, tmp)
+                if (tmp->flags & flag)
+                        sd = tmp;
+
+        while (sd) {
+                cpumask_t span;
+                struct sched_group *group;
+                int new_cpu;
+                int weight;
+
+                span = sd->span;
+                group = find_idlest_group(sd, t, cpu);
+                if (!group)
+                        goto nextlevel;
+
+                new_cpu = find_idlest_cpu(group, cpu);
+                if (new_cpu == -1 || new_cpu == cpu)
+                        goto nextlevel;
+
+                /* Now try balancing at a lower domain level */
+                cpu = new_cpu;
+nextlevel:
+                sd = NULL;
+                weight = cpus_weight(span);
+                for_each_domain(cpu, tmp) {
+                        if (weight <= cpus_weight(tmp->span))
+                                break;
+                        if (tmp->flags & flag)
+                                sd = tmp;
+                }
+                /* while loop will break here if sd == NULL */
+        }
+
+        return cpu;
+}
+
+#endif /* CONFIG_SMP */
 
 /*
  * wake_idle() will wake a task on an idle cpu if task->cpu is
@@ -1240,8 +1291,15 @@ int fastcall wake_up_state(task_t *p, unsigned int state)
  * Perform scheduler related setup for a newly forked process p.
  * p is forked by current.
  */
-void fastcall sched_fork(task_t *p)
+void fastcall sched_fork(task_t *p, int clone_flags)
 {
+        int cpu = get_cpu();
+
+#ifdef CONFIG_SMP
+        cpu = sched_balance_self(cpu, SD_BALANCE_FORK);
+#endif
+        set_task_cpu(p, cpu);
+
         /*
          * We mark the process as running here, but have not actually
          * inserted it onto the runqueue yet. This guarantees that
@@ -1282,12 +1340,10 @@ void fastcall sched_fork(task_t *p)
                  * runqueue lock is not a problem.
                  */
                 current->time_slice = 1;
-                preempt_disable();
                 scheduler_tick();
-                local_irq_enable();
-                preempt_enable();
-        } else
-                local_irq_enable();
+        }
+        local_irq_enable();
+        put_cpu();
 }
 
 /*
@@ -1302,64 +1358,12 @@ void fastcall wake_up_new_task(task_t * p, unsigned long clone_flags)
         unsigned long flags;
         int this_cpu, cpu;
         runqueue_t *rq, *this_rq;
-#ifdef CONFIG_SMP
-        struct sched_domain *tmp, *sd = NULL;
-#endif
 
         rq = task_rq_lock(p, &flags);
         BUG_ON(p->state != TASK_RUNNING);
         this_cpu = smp_processor_id();
         cpu = task_cpu(p);
 
-#ifdef CONFIG_SMP
-        for_each_domain(cpu, tmp)
-                if (tmp->flags & SD_BALANCE_FORK)
-                        sd = tmp;
-
-        if (sd) {
-                cpumask_t span;
-                int new_cpu;
-                struct sched_group *group;
-
-again:
-                schedstat_inc(sd, sbf_cnt);
-                span = sd->span;
-                cpu = task_cpu(p);
-                group = find_idlest_group(sd, p, cpu);
-                if (!group) {
-                        schedstat_inc(sd, sbf_balanced);
-                        goto nextlevel;
-                }
-
-                new_cpu = find_idlest_cpu(group, cpu);
-                if (new_cpu == -1 || new_cpu == cpu) {
-                        schedstat_inc(sd, sbf_balanced);
-                        goto nextlevel;
-                }
-
-                if (cpu_isset(new_cpu, p->cpus_allowed)) {
-                        schedstat_inc(sd, sbf_pushed);
-                        set_task_cpu(p, new_cpu);
-                        task_rq_unlock(rq, &flags);
-                        rq = task_rq_lock(p, &flags);
-                        cpu = task_cpu(p);
-                }
-
-                /* Now try balancing at a lower domain level */
-nextlevel:
-                sd = NULL;
-                for_each_domain(cpu, tmp) {
-                        if (cpus_subset(span, tmp->span))
-                                break;
-                        if (tmp->flags & SD_BALANCE_FORK)
-                                sd = tmp;
-                }
-
-                if (sd)
-                        goto again;
-        }
-
-#endif
         /*
          * We decrease the sleep average of forking parents
          * and children as well, to keep max-interactive tasks
@@ -1708,58 +1712,16 @@ out:
 }
 
 /*
- * sched_exec(): find the highest-level, exec-balance-capable
- * domain and try to migrate the task to the least loaded CPU.
- *
- * execve() is a valuable balancing opportunity, because at this point
- * the task has the smallest effective memory and cache footprint.
+ * sched_exec - execve() is a valuable balancing opportunity, because at
+ * this point the task has the smallest effective memory and cache footprint.
  */
 void sched_exec(void)
 {
-        struct sched_domain *tmp, *sd = NULL;
         int new_cpu, this_cpu = get_cpu();
-
-        for_each_domain(this_cpu, tmp)
-                if (tmp->flags & SD_BALANCE_EXEC)
-                        sd = tmp;
-
-        if (sd) {
-                cpumask_t span;
-                struct sched_group *group;
-again:
-                schedstat_inc(sd, sbe_cnt);
-                span = sd->span;
-                group = find_idlest_group(sd, current, this_cpu);
-                if (!group) {
-                        schedstat_inc(sd, sbe_balanced);
-                        goto nextlevel;
-                }
-                new_cpu = find_idlest_cpu(group, this_cpu);
-                if (new_cpu == -1 || new_cpu == this_cpu) {
-                        schedstat_inc(sd, sbe_balanced);
-                        goto nextlevel;
-                }
-
-                schedstat_inc(sd, sbe_pushed);
-                put_cpu();
-                sched_migrate_task(current, new_cpu);
-
-                /* Now try balancing at a lower domain level */
-                this_cpu = get_cpu();
-nextlevel:
-                sd = NULL;
-                for_each_domain(this_cpu, tmp) {
-                        if (cpus_subset(span, tmp->span))
-                                break;
-                        if (tmp->flags & SD_BALANCE_EXEC)
-                                sd = tmp;
-                }
-
-                if (sd)
-                        goto again;
-        }
-
+        new_cpu = sched_balance_self(this_cpu, SD_BALANCE_EXEC);
         put_cpu();
+        if (new_cpu != this_cpu)
+                sched_migrate_task(current, new_cpu);
 }
 
 /*