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Subject[PATCH v2 18/19] sched/numa: Reset scan rate whenever task moves across nodes
Date
Currently task scan rate is reset when numa balancer migrates the task
to a different node. If numa balancer initiates a swap, reset is only
applicable to the task that initiates the swap. Similarly no scan rate
reset is done if the task is migrated across nodes by traditional load
balancer.

Instead move the scan reset to the migrate_task_rq. This ensures the
task moved out of its preferred node, either gets back to its preferred
node quickly or finds a new preferred node. Doing so, would be fair to
all tasks migrating across nodes.

Running SPECjbb2005 on a 4 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
16 26251.7 25862.6 -1.48
1 74108 74357 0.335

Running SPECjbb2005 on a 16 node machine and comparing bops/JVM
JVMS LAST_PATCH WITH_PATCH %CHANGE
8 120453 117019 -2.85
1 181140 179095 -1.12

(numbers from v1 based on v4.17-rc5)
Testcase Time: Min Max Avg StdDev
numa01.sh Real: 428.48 837.17 700.45 162.77
numa01.sh Sys: 78.64 247.70 164.45 58.32
numa01.sh User: 37487.25 63728.06 54399.27 10088.13
numa02.sh Real: 60.07 62.65 61.41 0.85
numa02.sh Sys: 15.83 29.36 21.04 4.48
numa02.sh User: 5194.27 5280.60 5236.55 28.01
numa03.sh Real: 814.33 881.93 849.69 27.06
numa03.sh Sys: 111.45 134.02 125.28 7.69
numa03.sh User: 63007.36 68013.46 65590.46 2023.37
numa04.sh Real: 412.19 438.75 424.43 9.28
numa04.sh Sys: 232.97 315.77 268.98 26.98
numa04.sh User: 33997.30 35292.88 34711.66 415.78
numa05.sh Real: 394.88 449.45 424.30 22.53
numa05.sh Sys: 262.03 390.10 314.53 51.01
numa05.sh User: 33389.03 35684.40 34561.34 942.34

Testcase Time: Min Max Avg StdDev %Change
numa01.sh Real: 449.46 770.77 615.22 101.70 13.85%
numa01.sh Sys: 132.72 208.17 170.46 24.96 -3.52%
numa01.sh User: 39185.26 60290.89 50066.76 6807.84 8.653%
numa02.sh Real: 60.85 61.79 61.28 0.37 0.212%
numa02.sh Sys: 15.34 24.71 21.08 3.61 -0.18%
numa02.sh User: 5204.41 5249.85 5231.21 17.60 0.102%
numa03.sh Real: 785.50 916.97 840.77 44.98 1.060%
numa03.sh Sys: 108.08 133.60 119.43 8.82 4.898%
numa03.sh User: 61422.86 70919.75 64720.87 3310.61 1.343%
numa04.sh Real: 429.57 587.37 480.80 57.40 -11.7%
numa04.sh Sys: 240.61 321.97 290.84 33.58 -7.51%
numa04.sh User: 34597.65 40498.99 37079.48 2060.72 -6.38%
numa05.sh Real: 392.09 431.25 414.65 13.82 2.327%
numa05.sh Sys: 229.41 372.48 297.54 53.14 5.710%
numa05.sh User: 33390.86 34697.49 34222.43 556.42 0.990%

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
kernel/sched/fair.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7350f09..36d1414 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1807,12 +1807,6 @@ static int task_numa_migrate(struct task_struct *p)
if (env.best_cpu == -1)
return -EAGAIN;

- /*
- * Reset the scan period if the task is being rescheduled on an
- * alternative node to recheck if the tasks is now properly placed.
- */
- p->numa_scan_period = task_scan_start(p);
-
best_rq = cpu_rq(env.best_cpu);
if (env.best_task == NULL) {
pg_data_t *pgdat = NODE_DATA(cpu_to_node(env.dst_cpu));
@@ -6668,6 +6662,19 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu __maybe_unus

/* We have migrated, no longer consider this task hot */
p->se.exec_start = 0;
+
+#ifdef CONFIG_NUMA_BALANCING
+ if (!p->mm || (p->flags & PF_EXITING))
+ return;
+
+ if (p->numa_faults) {
+ int src_nid = cpu_to_node(task_cpu(p));
+ int dst_nid = cpu_to_node(new_cpu);
+
+ if (src_nid != dst_nid)
+ p->numa_scan_period = task_scan_start(p);
+ }
+#endif
}

static void task_dead_fair(struct task_struct *p)
--
1.8.3.1
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