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

[tip-bot for Aravind Gopalakrishnan]

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:

  http://marc.info/?l=linux-kernel&m=141279712429834&w=2

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

  http://marc.info/?l=linux-kernel&m=141353106106771&w=2

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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