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Subject[PATCH 5/6] 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.

specjbb2005 / bops/JVM / higher bops are better
on 2 Socket/2 Node Intel
JVMS Prev Current %Change
4 210118 208862 -0.597759
1 313171 307007 -1.96825


on 2 Socket/4 Node Power8 (PowerNV)
JVMS Prev Current %Change
8 91027.5 89911.4 -1.22611
1 216460 216176 -0.131202


on 2 Socket/2 Node Power9 (PowerNV)
JVMS Prev Current %Change
4 191918 196078 2.16759
1 207043 214664 3.68088


on 4 Socket/4 Node Power7
JVMS Prev Current %Change
8 58462.1 60719.2 3.86079
1 108334 112615 3.95167


dbench / transactions / higher numbers are better
on 2 Socket/2 Node Intel
count Min Max Avg Variance %Change
5 11851.8 11937.3 11890.9 33.5169
5 12511.7 12559.4 12539.5 15.5883 5.45459


on 2 Socket/4 Node Power8 (PowerNV)
count Min Max Avg Variance %Change
5 4791 5016.08 4962.55 85.9625
5 4709.28 4979.28 4919.32 105.126 -0.871125


on 2 Socket/2 Node Power9 (PowerNV)
count Min Max Avg Variance %Change
5 9353.43 9380.49 9369.6 9.04361
5 9388.38 9406.29 9395.1 5.98959 0.272157


on 4 Socket/4 Node Power7
count Min Max Avg Variance %Change
5 149.518 215.412 179.083 21.5903
5 157.71 184.929 174.754 10.7275 -2.41731

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 a5936ed..4ea0eff 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1837,12 +1837,6 @@ 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) {
ret = migrate_task_to(p, env.best_cpu);
@@ -6361,6 +6355,19 @@ 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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