linux-kernel - [PATCH] sched/numa: Fix NUMA_DIRECT topology identification

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Date:	Mon, 10 Aug 2015 20:20:48 -0500
From:	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>
To:	<mingo@...hat.com>, <peterz@...radead.org>,
	<linux-kernel@...r.kernel.org>
CC:	<riel@...hat.com>
Subject: [PATCH] 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@....com>
---
 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 655557d..e51739e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6442,8 +6442,10 @@ 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) {
-- 
2.4.0

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