linux-kernel - [tip:sched/urgent] sched/numa: Load balance between remote nodes

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Date:	Wed, 6 Jun 2012 08:53:25 -0700
From:	tip-bot for Alex Shi <alex.shi@...el.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	a.p.zijlstra@...llo.nl, alex.shi@...el.com, tglx@...utronix.de
Subject: [tip:sched/urgent] sched/numa: Load balance between remote nodes

Commit-ID:  10717dcde10d09f9fcee53a12a4236af1a82b484
Gitweb:     http://git.kernel.org/tip/10717dcde10d09f9fcee53a12a4236af1a82b484
Author:     Alex Shi <alex.shi@...el.com>
AuthorDate: Wed, 6 Jun 2012 14:52:51 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 6 Jun 2012 16:52:25 +0200

sched/numa: Load balance between remote nodes

Commit cb83b629b ("sched/numa: Rewrite the CONFIG_NUMA sched
domain support") removed the NODE sched domain and started checking
if the node distance in SLIT table is farther than REMOTE_DISTANCE,
if so, it will lose the load balance chance at exec/fork/wake_affine
points.

But actually, even the node distance is farther than REMOTE_DISTANCE.

Modern CPUs also has QPI like connections, which ensures that memory
access is not too slow between nodes. So the above change in behavior
on NUMA machine causes a performance regression on various benchmarks:
hackbench, tbench, netperf, oltp, etc.

This patch will recover the scheduler behavior to old mode on all my
Intel platforms: NHM EP/EX, WSM EP, SNB EP/EP4S, and thus fixes the
perfromance regressions. (all of them just have 2 kinds distance, 10, 21)

Signed-off-by: Alex Shi <alex.shi@...el.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1338965571-9812-1-git-send-email-alex.shi@intel.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/core.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c46958e..6546083 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6321,7 +6321,7 @@ static int sched_domains_curr_level;

 static inline int sd_local_flags(int level)
 {
-	if (sched_domains_numa_distance[level] > REMOTE_DISTANCE)
+	if (sched_domains_numa_distance[level] > RECLAIM_DISTANCE)
 		return 0;

 	return SD_BALANCE_EXEC | SD_BALANCE_FORK | SD_WAKE_AFFINE;
--
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