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Subject[patch 5/5] sched: consolidate sbe sbf
5/5

Any ideas about what to do with schedstats?
Do we really need balance on exec and fork as seperate
statistics?
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>

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c 2005-04-05 18:39:14.000000000 +1000
+++ linux-2.6/kernel/sched.c 2005-04-05 18:40:18.000000000 +1000
@@ -1013,8 +1013,57 @@ static int find_idlest_cpu(struct sched_
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;
+
+ 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;
+ for_each_domain(cpu, tmp) {
+ if (cpus_subset(span, 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
@@ -1295,63 +1344,22 @@ void fastcall wake_up_new_task(task_t *
int this_cpu, cpu;
runqueue_t *rq, *this_rq;
#ifdef CONFIG_SMP
- struct sched_domain *tmp, *sd = NULL;
-#endif
+ int new_cpu;

+ cpu = task_cpu(p);
+ preempt_disable();
+ new_cpu = sched_balance_self(cpu, SD_BALANCE_FORK);
+ preempt_enable();
+ if (new_cpu != cpu)
+ set_task_cpu(p, new_cpu);
+#endif
+
+ cpu = task_cpu(p);
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;
- }
+ BUG_ON(p->state != TASK_RUNNING);

-#endif
/*
* We decrease the sleep average of forking parents
* and children as well, to keep max-interactive tasks
@@ -1699,59 +1707,17 @@ out:
task_rq_unlock(rq, &flags);
}

-/*
- * 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);
}

/*
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