[tip:sched/core] sched/numa: Fix NUMA_DIRECT topology identification

From: tip-bot for Aravind Gopalakrishnan
Date: Wed Aug 12 2015 - 08:38:18 EST

Commit-ID: e237882b8f83dd1a0eece1608bcb689d4f4b221b
Gitweb: http://git.kernel.org/tip/e237882b8f83dd1a0eece1608bcb689d4f4b221b
Author: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>
AuthorDate: Mon, 10 Aug 2015 20:20:48 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 12 Aug 2015 12:06:08 +0200

sched/numa: Fix NUMA_DIRECT topology identification

Systems which have all nodes at a distance of at most 1 hop should be
identified as 'NUMA_DIRECT'.

However, the scheduler incorrectly identifies it as 'NUMA_BACKPLANE'.
This is because 'n' is assigned to sched_max_numa_distance but the
code (mis)interprets it to mean 'number of hops'.

Rik had actually used sched_domains_numa_levels for detecting a
'NUMA_DIRECT' topology:


But that was changed when he removed the hops table in the
subsequent version:


Fixing the issue here.

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@xxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Mike Galbraith <efault@xxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/1439256048-3748-1-git-send-email-Aravind.Gopalakrishnan@xxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
kernel/sched/core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b11f624..ea6d743 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6444,8 +6444,10 @@ static void init_numa_topology_type(void)

n = sched_max_numa_distance;

- if (n <= 1)
+ if (sched_domains_numa_levels <= 1) {
sched_numa_topology_type = NUMA_DIRECT;
+ return;
+ }

for_each_online_node(a) {
for_each_online_node(b) {
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