Commit 74a5ce20 authored May 23, 2012 by Peter Zijlstra Committed by Ingo Molnar May 30, 2012

sched: Fix SD_OVERLAP



SD_OVERLAP exists to allow overlapping groups, overlapping groups
appear in NUMA topologies that aren't fully connected.

The typical result of not fully connected NUMA is that each cpu (or
rather node) will have different spans for a particular distance.
However due to how sched domains are traversed -- only the first cpu
in the mask goes one level up -- the next level only cares about the
spans of the cpus that went up.

Due to this two things were observed to be broken:

 - build_overlap_sched_groups() -- since its possible the cpu we're
   building the groups for exists in multiple (or all) groups, the
   selection criteria of the first group didn't ensure there was a cpu
   for which is was true that cpumask_first(span) == cpu. Thus load-
   balancing would terminate.

 - update_group_power() -- assumed that the cpu span of the first
   group of the domain was covered by all groups of the child domain.
   The above explains why this isn't true, so deal with it.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Rientjes <rientjes@google.com>
Link: http://lkml.kernel.org/r/1337788843.9783.14.camel@laptop


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 2ea45800

kernel/sched/core.c

+5 −2

Original line number	Diff line number	Diff line
		@@ -6030,11 +6030,14 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu)

		cpumask_or(covered, covered, sg_span);

		sg->sgp = *per_cpu_ptr(sdd->sgp, cpumask_first(sg_span));
		sg->sgp = *per_cpu_ptr(sdd->sgp, i);
		atomic_inc(&sg->sgp->ref);

		if (cpumask_test_cpu(cpu, sg_span))
		if ((!groups && cpumask_test_cpu(cpu, sg_span)) \|\|
		cpumask_first(sg_span) == cpu) {
		WARN_ON_ONCE(!cpumask_test_cpu(cpu, sg_span));
		groups = sg;
		}

		if (!first)
		first = sg;

kernel/sched/fair.c

+20 −5

Original line number	Diff line number	Diff line
		@@ -3574,11 +3574,26 @@ void update_group_power(struct sched_domain *sd, int cpu)

		power = 0;

		if (child->flags & SD_OVERLAP) {
		/*
		* SD_OVERLAP domains cannot assume that child groups
		* span the current group.
		*/

		for_each_cpu(cpu, sched_group_cpus(sdg))
		power += power_of(cpu);
		} else {
		/*
		* !SD_OVERLAP domains can assume that child groups
		* span the current group.
		*/

		group = child->groups;
		do {
		power += group->sgp->power;
		group = group->next;
		} while (group != child->groups);
		}

		sdg->sgp->power = power;
		}

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