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Subject[tip:sched/core] sched/numa: Set preferred_node based on best_cpu
Commit-ID:  8cd45eee43bd46b933158b25aa7c742e0f3e811f
Gitweb: https://git.kernel.org/tip/8cd45eee43bd46b933158b25aa7c742e0f3e811f
Author: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
AuthorDate: Wed, 20 Jun 2018 22:32:45 +0530
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 25 Jul 2018 11:41:06 +0200

sched/numa: Set preferred_node based on best_cpu

Currently preferred node is set to dst_nid which is the last node in the
iteration whose group weight or task weight is greater than the current
node. However it doesn't guarantee that dst_nid has the numa capacity
to move. It also doesn't guarantee that dst_nid has the best_cpu which
is the CPU/node ideal for node migration.

Lets consider faults on a 4 node system with group weight numbers
in different nodes being in 0 < 1 < 2 < 3 proportion. Consider the task
is running on 3 and 0 is its preferred node but its capacity is full.
Consider nodes 1, 2 and 3 have capacity. Then the task should be
migrated to node 1. Currently the task gets moved to node 2. env.dst_nid
points to the last node whose faults were greater than current node.

Modify to set the preferred node based of best_cpu. Earlier setting
preferred node was skipped if nr_active_nodes is 1. This could result in
the task being moved out of the preferred node to a random node during
regular load balancing.

Also while modifying task_numa_migrate(), use sched_setnuma to set
preferred node. This ensures out numa accounting is correct.

Running SPECjbb2005 on a 4 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
16 25122.9 25549.6 1.698
1 73850 73190 -0.89

Running SPECjbb2005 on a 16 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
8 105930 113437 7.08676
1 178624 196130 9.80047

(numbers from v1 based on v4.17-rc5)
Testcase Time: Min Max Avg StdDev
numa01.sh Real: 435.78 653.81 534.58 83.20
numa01.sh Sys: 121.93 187.18 145.90 23.47
numa01.sh User: 37082.81 51402.80 43647.60 5409.75
numa02.sh Real: 60.64 61.63 61.19 0.40
numa02.sh Sys: 14.72 25.68 19.06 4.03
numa02.sh User: 5210.95 5266.69 5233.30 20.82
numa03.sh Real: 746.51 808.24 780.36 23.88
numa03.sh Sys: 97.26 108.48 105.07 4.28
numa03.sh User: 58956.30 61397.05 60162.95 1050.82
numa04.sh Real: 465.97 519.27 484.81 19.62
numa04.sh Sys: 304.43 359.08 334.68 20.64
numa04.sh User: 37544.16 41186.15 39262.44 1314.91
numa05.sh Real: 411.57 457.20 433.29 16.58
numa05.sh Sys: 230.05 435.48 339.95 67.58
numa05.sh User: 33325.54 36896.31 35637.84 1222.64

Testcase Time: Min Max Avg StdDev %Change
numa01.sh Real: 506.35 794.46 599.06 104.26 -10.76%
numa01.sh Sys: 150.37 223.56 195.99 24.94 -25.55%
numa01.sh User: 43450.69 61752.04 49281.50 6635.33 -11.43%
numa02.sh Real: 60.33 62.40 61.31 0.90 -0.195%
numa02.sh Sys: 18.12 31.66 24.28 5.89 -21.49%
numa02.sh User: 5203.91 5325.32 5260.29 49.98 -0.513%
numa03.sh Real: 696.47 853.62 745.80 57.28 4.6339%
numa03.sh Sys: 85.68 123.71 97.89 13.48 7.3347%
numa03.sh User: 55978.45 66418.63 59254.94 3737.97 1.5323%
numa04.sh Real: 444.05 514.83 497.06 26.85 -2.464%
numa04.sh Sys: 230.39 375.79 316.23 48.58 5.8343%
numa04.sh User: 35403.12 41004.10 39720.80 2163.08 -1.153%
numa05.sh Real: 423.09 460.41 439.57 13.92 -1.428%
numa05.sh Sys: 287.38 480.15 369.37 68.52 -7.964%
numa05.sh User: 34732.12 38016.80 36255.85 1070.51 -1.704%

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1529514181-9842-5-git-send-email-srikar@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/sched/fair.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 226837960ec0..0532195c38d0 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1765,7 +1765,7 @@ static int task_numa_migrate(struct task_struct *p)
* elsewhere, so there is no point in (re)trying.
*/
if (unlikely(!sd)) {
- p->numa_preferred_nid = task_node(p);
+ sched_setnuma(p, task_node(p));
return -EINVAL;
}

@@ -1824,15 +1824,13 @@ static int task_numa_migrate(struct task_struct *p)
* trying for a better one later. Do not set the preferred node here.
*/
if (p->numa_group) {
- struct numa_group *ng = p->numa_group;
-
if (env.best_cpu == -1)
nid = env.src_nid;
else
- nid = env.dst_nid;
+ nid = cpu_to_node(env.best_cpu);

- if (ng->active_nodes > 1 && numa_is_active_node(env.dst_nid, ng))
- sched_setnuma(p, env.dst_nid);
+ if (nid != p->numa_preferred_nid)
+ sched_setnuma(p, nid);
}

/* No better CPU than the current one was found. */
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