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Subject[Patch] sched: remove unnecessary sched domains
Appended patch removes the unnecessary scheduler domains(containing
only one sched group) setup during the sched-domain init.

For example on x86_64, we always have NUMA configured in. On Intel EM64T
systems, top most sched domain will be of NUMA and with only one sched_group in

With fork/exec balances(recent Nick's fixes in -mm tree), we always endup
taking wrong decisions because of this topmost domain (as it contains only
one group and find_idlest_group always returns NULL). We will endup loading
HT package completely first, letting active load balance kickin and correct it.

In general, this patch also makes sense with out recent Nick's fixes
in -mm.

Signed-off-by: Suresh Siddha <>

--- linux-2.6.12-rc1-mm4/kernel/sched.c 2005-04-01 10:07:24.183605296 -0800
+++ linux/kernel/sched.c 2005-04-01 15:29:28.274896888 -0800
@@ -4748,6 +4748,21 @@
unsigned long flags;
runqueue_t *rq = cpu_rq(cpu);
int local = 1;
+ struct sched_domain *tmp = sd, *tmp1;
+ /* Remove the sched domains which has only one group
+ */
+ while (tmp) {
+ tmp1 = tmp->parent;
+ if (!tmp1)
+ break;
+ if (tmp1->groups == tmp1->groups->next)
+ tmp->parent = tmp1->parent;
+ tmp = tmp->parent;
+ }
+ if (sd->parent && sd->groups && sd->groups == sd->groups->next)
+ sd = sd->parent;

sched_domain_debug(sd, cpu);

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