relax_domain_level boot parameter has no effect

I noticed (and verified) that the relax_domain_level boot parameter does not get processed because sched_domain_level_max is 0 at the time that setup_relax_domain_level() is run.

int sched_domain_level_max;

static int __init setup_relax_domain_level(char *str)

{
        unsigned long val;

        val = simple_strtoul(str, NULL, 0);
        if (val < sched_domain_level_max)
                default_relax_domain_level = val;

        return 1;
}

__setup("relax_domain_level=", setup_relax_domain_level);

struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl, ..

                sched_domain_level_max = max(sched_domain_level_max, sd->level);

..

Ah indeed.. this has been so for a while I guess.

What are you using this knob for?

On a very related note, the sched_relax_domain_level setting in cpuset doesn't appear to work correctly either (if I'm interpreting all of this correctly).

The reason is that the build_sched_domain() routine calls the set_domain_attribute() routine prior to setting the sd->level, however, the set_domain_attribute() routine relies on the sd->level to decide whether idle load balancing will be off/on.

static void set_domain_attribute(struct sched_domain *sd, ..

==>     if (request < sd->level) {
                /* turn off idle balance on this domain */

..
..
struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl, ..

==>     set_domain_attribute(sd, attr);
        cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu));
        if (child) {
==>             sd->level = child->level + 1;
                sched_domain_level_max = max(sched_domain_level_max, sd->level);

I was poking around for different ways to turn off idle load balancing when I ran into all of this.

I'll submit a patch shortly that should return these back to what appears to be their intended functionality.

I guess removing the max check in the paramater parsing is the easiest thing.

My thoughts exactly.

Fix the relax_domain_level boot parameter. It does not get processed because sched_domain_level_max is 0 at the time that setup_relax_domain_level() is run. Simply accept the value as it is, as we don't know the value of sched_domain_level_max until sched domain construction is completed.

Fix sched_relax_domain_level in cpuset. The build_sched_domain() routine calls the set_domain_attribute() routine prior to setting the sd->level, however, the set_domain_attribute() routine relies on the sd->level to decide whether idle load balancing will be off/on.

---
 kernel/sched/core.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

Index: linux/kernel/sched/core.c
===================================================================
@@ -6165,11 +6165,8 @@ int sched_domain_level_max;
 
 static int __init setup_relax_domain_level(char *str)
 {
-	unsigned long val;
-
-	val = simple_strtoul(str, NULL, 0);
-	if (val < sched_domain_level_max)
-		default_relax_domain_level = val;
+	if (kstrtoint(str, 0, &default_relax_domain_level))
+		pr_warn("Unable to set relax_domain_level\n");
 
 	return 1;
 }

@@ -6543,7 +6540,6 @@ struct sched_domain *build_sched_domain(
 	if (!sd)
 		return child;
 
-	set_domain_attribute(sd, attr);
 	cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu));
 	if (child) {
 		sd->level = child->level + 1;

@@ -6551,6 +6547,7 @@ struct sched_domain *build_sched_domain(
 		child->parent = sd;
 	}
 	sd->child = child;
+	set_domain_attribute(sd, attr);
 
 	return sd;
 }

Commit-ID:  a841f8cef4bb124f0f5563314d0beaf2e1249d72
Gitweb:     http://git.kernel.org/tip/a841f8cef4bb124f0f5563314d0beaf2e1249d72
Author:     Dimitri Sivanich <[email protected]>
AuthorDate: Tue, 5 Jun 2012 13:44:36 -0500
Committer:  Ingo Molnar <[email protected]>
CommitDate: Wed, 6 Jun 2012 17:07:41 +0200

sched: Fix the relax_domain_level boot parameter

It does not get processed because sched_domain_level_max is 0 at the time that setup_relax_domain_level() is run.

Simply accept the value as it is, as we don't know the value of sched_domain_level_max until sched domain construction is completed.

Fix sched_relax_domain_level in cpuset. The build_sched_domain() routine calls the set_domain_attribute() routine prior to setting the sd->level, however, the set_domain_attribute() routine relies on the sd->level to decide whether idle load balancing will be off/on.

---
 kernel/sched/core.c |    9 +++------
 1 files changed, 3 insertions(+), 6 deletions(-)

index 2bdd176..d5594a4 100644
@@ -6268,11 +6268,8 @@ int sched_domain_level_max;
 
 static int __init setup_relax_domain_level(char *str)
 {
-	unsigned long val;
-
-	val = simple_strtoul(str, NULL, 0);
-	if (val < sched_domain_level_max)
-		default_relax_domain_level = val;
+	if (kstrtoint(str, 0, &default_relax_domain_level))
+		pr_warn("Unable to set relax_domain_level\n");
 
 	return 1;
 }

@@ -6698,7 +6695,6 @@ struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl,
 	if (!sd)
 		return child;
 
-	set_domain_attribute(sd, attr);
 	cpumask_and(sched_domain_span(sd), cpu_map, tl->mask(cpu));
 	if (child) {
 		sd->level = child->level + 1;

@@ -6706,6 +6702,7 @@ struct sched_domain *build_sched_domain(struct sched_domain_topology_level *tl,
 		child->parent = sd;
 	}
 	sd->child = child;
+	set_domain_attribute(sd, attr);
 
 	return sd;
 }