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[PATCH 03/14] sched/topology: Fix building of overlapping sched-groups

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  [PATCH 03/14] sched/topology: Fix building of overlapping sched-groups Peter Zijlstra <peterz@infradead.org> - 2017-04-28 15:40 +0200
    Re: [PATCH 03/14] sched/topology: Fix building of overlapping  sched-groups Rik van Riel <riel@redhat.com> - 2017-05-01 22:10 +0200

#1632889 — [PATCH 03/14] sched/topology: Fix building of overlapping sched-groups

When building the overlapping groups, we very obviously should start
with the previous domain of _this_ @cpu, not CPU-0.

This can be readily demonstrated with a topology like:

  node   0   1   2   3
    0:  10  20  30  20
    1:  20  10  20  30
    2:  30  20  10  20
    3:  20  30  20  10

Where (for example) CPU1 ends up generating the following nonsensical groups:

  [] CPU1 attaching sched-domain:
  []  domain 0: span 0-2 level NUMA
  []   groups: 1 2 0
  []   domain 1: span 0-3 level NUMA
  []    groups: 1-3 (cpu_capacity = 3072) 0-1,3 (cpu_capacity = 3072)

Where the fact that domain 1 doesn't include a group with span 0-2 is
the obvious fail.

With patch this looks like:

  [] CPU1 attaching sched-domain:
  []  domain 0: span 0-2 level NUMA
  []   groups: 1 0 2
  []   domain 1: span 0-3 level NUMA
  []    groups: 0-2 (cpu_capacity = 3072) 0,2-3 (cpu_capacity = 3072)

Cc: stable@vger.kernel.org
Fixes: e3589f6c81e4 ("sched: Allow for overlapping sched_domain spans")
Debugged-by: Lauro Ramos Venancio <lvenanci@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/topology.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -525,7 +525,7 @@ build_overlap_sched_groups(struct sched_
 
 	cpumask_clear(covered);
 
-	for_each_cpu(i, span) {
+	for_each_cpu_wrap(i, span, cpu) {
 		struct cpumask *sg_span;
 
 		if (cpumask_test_cpu(i, covered))

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#1633848 — Re: [PATCH 03/14] sched/topology: Fix building of overlapping sched-groups

On Fri, 2017-04-28 at 15:20 +0200, Peter Zijlstra wrote:
> When building the overlapping groups, we very obviously should start
> with the previous domain of _this_ @cpu, not CPU-0.

> With patch this looks like:
> 
>   [] CPU1 attaching sched-domain:
>   []  domain 0: span 0-2 level NUMA
>   []   groups: 1 0 2
>   []   domain 1: span 0-3 level NUMA
>   []    groups: 0-2 (cpu_capacity = 3072) 0,2-3 (cpu_capacity = 3072)
> 
> Cc: stable@vger.kernel.org
> Fixes: e3589f6c81e4 ("sched: Allow for overlapping sched_domain
> spans")
> Debugged-by: Lauro Ramos Venancio <lvenanci@redhat.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Acked-by: Rik van Riel <riel@redhat.com>

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