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

From: Peter Zijlstra
Date: Fri Apr 28 2017 - 09:32:47 EST


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@xxxxxxxxxxxxxxx
Fixes: e3589f6c81e4 ("sched: Allow for overlapping sched_domain spans")
Debugged-by: Lauro Ramos Venancio <lvenanci@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
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))