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Subject[PATCH v2 15/19] sched/numa: Use group_weights to identify if migration degrades locality
Date
On NUMA_BACKPLANE and NUMA_GLUELESS_MESH systems, tasks/memory should be
consolidated to the closest group of nodes. In such a case, relying on
group_fault metric may not always help to consolidate. There can always
be a case where a node closer to the preferred node may have lesser
faults than a node further away from the preferred node. In such a case,
moving to node with more faults might avoid numa consolidation.

Using group_weight would help to consolidate task/memory around the
preferred_node.

While here, to be on the conservative side, don't override migrate thread
degrades locality logic for CPU_NEWLY_IDLE load balancing.

Note: Similar problems exist with should_numa_migrate_memory and will be
dealt separately.

Running SPECjbb2005 on a 4 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
16 25645.4 25960 1.22
1 72142 73550 1.95

Running SPECjbb2005 on a 16 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
8 110199 120071 8.958
1 176303 176249 -0.03

(numbers from v1 based on v4.17-rc5)
Testcase Time: Min Max Avg StdDev
numa01.sh Real: 490.04 774.86 596.26 96.46
numa01.sh Sys: 151.52 242.88 184.82 31.71
numa01.sh User: 41418.41 60844.59 48776.09 6564.27
numa02.sh Real: 60.14 62.94 60.98 1.00
numa02.sh Sys: 16.11 30.77 21.20 5.28
numa02.sh User: 5184.33 5311.09 5228.50 44.24
numa03.sh Real: 790.95 856.35 826.41 24.11
numa03.sh Sys: 114.93 118.85 117.05 1.63
numa03.sh User: 60990.99 64959.28 63470.43 1415.44
numa04.sh Real: 434.37 597.92 504.87 59.70
numa04.sh Sys: 237.63 397.40 289.74 55.98
numa04.sh User: 34854.87 41121.83 38572.52 2615.84
numa05.sh Real: 386.77 448.90 417.22 22.79
numa05.sh Sys: 149.23 379.95 303.04 79.55
numa05.sh User: 32951.76 35959.58 34562.18 1034.05

Testcase Time: Min Max Avg StdDev %Change
numa01.sh Real: 493.19 672.88 597.51 59.38 -0.20%
numa01.sh Sys: 150.09 245.48 207.76 34.26 -11.0%
numa01.sh User: 41928.51 53779.17 48747.06 3901.39 0.059%
numa02.sh Real: 60.63 62.87 61.22 0.83 -0.39%
numa02.sh Sys: 16.64 27.97 20.25 4.06 4.691%
numa02.sh User: 5222.92 5309.60 5254.03 29.98 -0.48%
numa03.sh Real: 821.52 902.15 863.60 32.41 -4.30%
numa03.sh Sys: 112.04 130.66 118.35 7.08 -1.09%
numa03.sh User: 62245.16 69165.14 66443.04 2450.32 -4.47%
numa04.sh Real: 414.53 519.57 476.25 37.00 6.009%
numa04.sh Sys: 181.84 335.67 280.41 54.07 3.327%
numa04.sh User: 33924.50 39115.39 37343.78 1934.26 3.290%
numa05.sh Real: 408.30 441.45 417.90 12.05 -0.16%
numa05.sh Sys: 233.41 381.60 295.58 57.37 2.523%
numa05.sh User: 33301.31 35972.50 34335.19 938.94 0.661%

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
kernel/sched/fair.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 711b533..9db09a6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7222,8 +7222,8 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
{
struct numa_group *numa_group = rcu_dereference(p->numa_group);
- unsigned long src_faults, dst_faults;
- int src_nid, dst_nid;
+ unsigned long src_weight, dst_weight;
+ int src_nid, dst_nid, dist;

if (!static_branch_likely(&sched_numa_balancing))
return -1;
@@ -7250,18 +7250,19 @@ static int migrate_degrades_locality(struct task_struct *p, struct lb_env *env)
return 0;

/* Leaving a core idle is often worse than degrading locality. */
- if (env->idle != CPU_NOT_IDLE)
+ if (env->idle == CPU_IDLE)
return -1;

+ dist = node_distance(src_nid, dst_nid);
if (numa_group) {
- src_faults = group_faults(p, src_nid);
- dst_faults = group_faults(p, dst_nid);
+ src_weight = group_weight(p, src_nid, dist);
+ dst_weight = group_weight(p, dst_nid, dist);
} else {
- src_faults = task_faults(p, src_nid);
- dst_faults = task_faults(p, dst_nid);
+ src_weight = task_weight(p, src_nid, dist);
+ dst_weight = task_weight(p, dst_nid, dist);
}

- return dst_faults < src_faults;
+ return dst_weight < src_weight;
}

#else
--
1.8.3.1
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