[PATCH v2 6/6] sched/numa: Avoid task migration for small NUMA improvement
From: Srikar Dronamraju
Date: Fri Sep 21 2018 - 13:49:57 EST
If NUMA improvement from the task migration is going to be very
minimal, then avoid task migration.
Specjbb2005 results (8 warehouses)
Higher bops are better
2 Socket - 2 Node Haswell - X86
JVMS Prev Current %Change
4 198512 205910 3.72673
1 313559 318491 1.57291
2 Socket - 4 Node Power8 - PowerNV
JVMS Prev Current %Change
8 74761.9 74935.9 0.232739
1 214874 226796 5.54837
2 Socket - 2 Node Power9 - PowerNV
JVMS Prev Current %Change
4 180536 189780 5.12031
1 210281 205695 -2.18089
4 Socket - 4 Node Power7 - PowerVM
JVMS Prev Current %Change
8 56511.4 60370 6.828
1 104899 108100 3.05151
1/7 cases is regressing, if we look at events migrate_pages seem
to vary the most especially in the regressing case. Also some
amount of variance is expected between different runs of
Specjbb2005.
Some events stats before and after applying the patch.
perf stats 8th warehouse Multi JVM 2 Socket - 2 Node Haswell - X86
Event Before After
cs 13,818,546 13,801,554
migrations 1,149,960 1,151,541
faults 385,583 433,246
cache-misses 55,259,546,768 55,168,691,835
sched:sched_move_numa 2,257 2,551
sched:sched_stick_numa 9 24
sched:sched_swap_numa 512 904
migrate:mm_migrate_pages 2,225 1,571
vmstat 8th warehouse Multi JVM 2 Socket - 2 Node Haswell - X86
Event Before After
numa_hint_faults 72692 113682
numa_hint_faults_local 62270 102163
numa_hit 238762 240181
numa_huge_pte_updates 48 36
numa_interleave 75 64
numa_local 238676 240103
numa_other 86 78
numa_pages_migrated 2225 1564
numa_pte_updates 98557 134080
perf stats 8th warehouse Single JVM 2 Socket - 2 Node Haswell - X86
Event Before After
cs 3,173,490 3,079,150
migrations 36,966 31,455
faults 108,776 99,081
cache-misses 12,200,075,320 11,588,126,740
sched:sched_move_numa 1,264 1
sched:sched_stick_numa 0 0
sched:sched_swap_numa 0 0
migrate:mm_migrate_pages 899 36
vmstat 8th warehouse Single JVM 2 Socket - 2 Node Haswell - X86
Event Before After
numa_hint_faults 21109 430
numa_hint_faults_local 17120 77
numa_hit 72934 71277
numa_huge_pte_updates 42 0
numa_interleave 33 22
numa_local 72866 71218
numa_other 68 59
numa_pages_migrated 915 23
numa_pte_updates 42326 0
perf stats 8th warehouse Multi JVM 2 Socket - 2 Node Power9 - PowerNV
Event Before After
cs 8,312,022 8,707,565
migrations 231,705 171,342
faults 310,242 310,820
cache-misses 402,324,573 136,115,400
sched:sched_move_numa 193 215
sched:sched_stick_numa 0 6
sched:sched_swap_numa 3 24
migrate:mm_migrate_pages 93 162
vmstat 8th warehouse Multi JVM 2 Socket - 2 Node Power9 - PowerNV
Event Before After
numa_hint_faults 11838 8985
numa_hint_faults_local 11216 8154
numa_hit 90689 93819
numa_huge_pte_updates 0 0
numa_interleave 1579 882
numa_local 89634 93496
numa_other 1055 323
numa_pages_migrated 92 169
numa_pte_updates 12109 9217
perf stats 8th warehouse Single JVM 2 Socket - 2 Node Power9 - PowerNV
Event Before After
cs 2,170,481 2,152,072
migrations 10,126 10,704
faults 160,962 164,376
cache-misses 10,834,845 3,818,437
sched:sched_move_numa 10 16
sched:sched_stick_numa 0 0
sched:sched_swap_numa 0 7
migrate:mm_migrate_pages 2 199
vmstat 8th warehouse Single JVM 2 Socket - 2 Node Power9 - PowerNV
Event Before After
numa_hint_faults 403 2248
numa_hint_faults_local 358 1666
numa_hit 25898 25704
numa_huge_pte_updates 0 0
numa_interleave 207 200
numa_local 25860 25679
numa_other 38 25
numa_pages_migrated 2 197
numa_pte_updates 400 2234
perf stats 8th warehouse Multi JVM 4 Socket - 4 Node Power7 - PowerVM
Event Before After
cs 110,339,633 93,330,595
migrations 4,139,812 4,122,061
faults 863,622 865,979
cache-misses 231,838,045,660 225,395,083,479
sched:sched_move_numa 2,196 2,372
sched:sched_stick_numa 33 24
sched:sched_swap_numa 544 769
migrate:mm_migrate_pages 2,469 1,677
vmstat 8th warehouse Multi JVM 4 Socket - 4 Node Power7 - PowerVM
Event Before After
numa_hint_faults 85748 91638
numa_hint_faults_local 66831 78096
numa_hit 242213 242225
numa_huge_pte_updates 0 0
numa_interleave 0 2
numa_local 242211 242219
numa_other 2 6
numa_pages_migrated 2376 1515
numa_pte_updates 86233 92274
perf stats 8th warehouse Single JVM 4 Socket - 4 Node Power7 - PowerVM
Event Before After
cs 59,331,057 51,487,271
migrations 552,019 537,170
faults 266,586 256,921
cache-misses 73,796,312,990 70,073,831,187
sched:sched_move_numa 981 576
sched:sched_stick_numa 54 24
sched:sched_swap_numa 286 327
migrate:mm_migrate_pages 713 726
vmstat 8th warehouse Single JVM 4 Socket - 4 Node Power7 - PowerVM
Event Before After
numa_hint_faults 14807 12000
numa_hint_faults_local 5738 5024
numa_hit 36230 36470
numa_huge_pte_updates 0 0
numa_interleave 0 0
numa_local 36228 36465
numa_other 2 5
numa_pages_migrated 703 726
numa_pte_updates 14742 11930
Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
Changelog v1->v2:
- Handle trivial changes due to variable name change. (Rik Van Riel)
- Drop changes where subsequent better CPU find was rejected for
small NUMA improvement (Rik Van Riel).
Changelog v3->v4:
- Refer cpu -> CPU
- Refer numa -> NUMA
kernel/sched/fair.c | 23 ++++++++++++++++++-----
1 file changed, 18 insertions(+), 5 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3529bf6..25c7c7e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1568,6 +1568,13 @@ static bool load_too_imbalanced(long src_load, long dst_load,
}
/*
+ * Maximum NUMA importance can be 1998 (2*999);
+ * SMALLIMP @ 30 would be close to 1998/64.
+ * Used to deter task migration.
+ */
+#define SMALLIMP 30
+
+/*
* This checks if the overall compute and NUMA accesses of the system would
* be improved if the source tasks was migrated to the target dst_cpu taking
* into account that it might be best if task running on the dst_cpu should
@@ -1600,7 +1607,7 @@ static void task_numa_compare(struct task_numa_env *env,
goto unlock;
if (!cur) {
- if (maymove || imp > env->best_imp)
+ if (maymove && moveimp >= env->best_imp)
goto assign;
else
goto unlock;
@@ -1643,16 +1650,22 @@ static void task_numa_compare(struct task_numa_env *env,
task_weight(cur, env->dst_nid, dist);
}
- if (imp <= env->best_imp)
- goto unlock;
-
if (maymove && moveimp > imp && moveimp > env->best_imp) {
- imp = moveimp - 1;
+ imp = moveimp;
cur = NULL;
goto assign;
}
/*
+ * If the NUMA importance is less than SMALLIMP,
+ * task migration might only result in ping pong
+ * of tasks and also hurt performance due to cache
+ * misses.
+ */
+ if (imp < SMALLIMP || imp <= env->best_imp + SMALLIMP / 2)
+ goto unlock;
+
+ /*
* In the overloaded case, try and keep the load balanced.
*/
load = task_h_load(env->p) - task_h_load(cur);
--
2.7.4