2015-08-11 01:03:09

by Aravind Gopalakrishnan

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 <[email protected]>
---
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

2015-08-11 01:07:05

by Rik van Riel

Subject: Re: [PATCH] sched/numa: Fix NUMA_DIRECT topology identification

On 08/10/2015 09:20 PM, Aravind Gopalakrishnan wrote:
> 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

Good catch! Thank you!

> Fixing the issue here.
>
> Signed-off-by: Aravind Gopalakrishnan <[email protected]>

Reviewed-by: Rik van Riel <[email protected]>

--
All rights reversed

2015-08-12 12:38:14

by tip-bot for Vasyl Gomonovych

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

Commit-ID: e237882b8f83dd1a0eece1608bcb689d4f4b221b
Gitweb: http://git.kernel.org/tip/e237882b8f83dd1a0eece1608bcb689d4f4b221b
Author: Aravind Gopalakrishnan <[email protected]>
AuthorDate: Mon, 10 Aug 2015 20:20:48 -0500
Committer: Ingo Molnar <[email protected]>
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 <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
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) {