Re: [PATCH 2.6.12-rc6-mm1] add allowed CPUs check into find_idlest_{group|cpu}()

[M.Baris Demiray]

Nick Piggin wrote:
> [...]
> Hi,

Hi Nick,

> [...]
> By taking the intersection in find_idlest_cpu, I don't mean checking
> whether or not they intersect as in find_idlest_group. I mean doing
> this:
>
>
>     cpumask_t tmp;
>
>     /* Find the intersection */
>     cpus_and(tmp, group->cpumask, p->cpus_allowed);
>
>     for_each_cpu_mask(i, tmp) {
>
> Right? That is effectively the same as what you've got in your patch,
> but it means we don't need to do the cpumask comparison every time
> around the loop (aside from being an extra branch, the actual operation
> itself gets a little costly with huge cpu masks).

You're right, I got it. Updated version is appended.

--- linux-2.6.12-rc6-mm1/kernel/sched.c.orig	2005-06-08 
00:28:59.000000000 +0000
+++ linux-2.6.12-rc6-mm1/kernel/sched.c	2005-06-08 20:45:25.000000000 +0000
@@ -1039,8 +1039,11 @@
 		int local_group;
 		int i;

+		/* Loop over if group has no CPUs allowed */
+		if (!cpus_intersects(group->cpumask, p->cpus_allowed))
+			continue;
+
 		local_group = cpu_isset(this_cpu, group->cpumask);
-		/* XXX: put a cpus allowed check */

 		/* Tally up the load of all CPUs in the group */
 		avg_load = 0;
@@ -1076,13 +1079,17 @@
 /*
  * find_idlest_queue - find the idlest runqueue among the cpus in group.
  */
-static int find_idlest_cpu(struct sched_group *group, int this_cpu)
+static int find_idlest_cpu(struct sched_group *group, struct 
task_struct *p,
+			   int this_cpu)
 {
 	unsigned long load, min_load = ULONG_MAX;
 	int idlest = -1;
 	int i;
+	cpumask_t allowed_cpus;

-	for_each_cpu_mask(i, group->cpumask) {
+	/* Traverse only the allowed CPUs */
+	cpus_and(allowed_cpus, group->cpumask, p->cpus_allowed);
+	for_each_cpu_mask(i, allowed_cpus) {
 		load = source_load(i, 0);

 		if (load < min_load || (load == min_load && i == this_cpu)) {
@@ -1124,7 +1131,7 @@
 		if (!group)
 			goto nextlevel;

-		new_cpu = find_idlest_cpu(group, cpu);
+		new_cpu = find_idlest_cpu(group, t, cpu);
 		if (new_cpu == -1 || new_cpu == cpu)
 			goto nextlevel;


PS: Thanks for your help and patience :-)

> Nick


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