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

["M.Baris Demiray" <baris@labristeknoloji.com>]

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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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