From: Ingo Molnar <mingo@kernel.org>

After this patch, doing:

   # echo NO_NUMA_MIGRATION > /sys/kernel/debug/sched_features

Will turn off the NUMA placement logic/policy - but keeps the
working set sampling faults in place.

This allows the debugging of the WSS facility, by using it
but keeping vanilla, non-NUMA CPU and memory placement
policies.

Default enabled. Generates on extra code on !CONFIG_SCHED_DEBUG.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <redacted>
Cc: Andrea Arcangeli <redacted>
Cc: Rik van Riel <redacted>
---
 kernel/sched/core.c     |    3 +++
 kernel/sched/features.h |    3 +++
 2 files changed, 6 insertions(+)

Index: tip/kernel/sched/core.c
===================================================================

--- tip.orig/kernel/sched/core.c
+++ tip/kernel/sched/core.c

@@ -6002,6 +6002,9 @@ void sched_setnode(struct task_struct *p
 	int on_rq, running;
 	struct rq *rq;
 
+	if (!sched_feat(NUMA_MIGRATION))
+		return;
+
 	rq = task_rq_lock(p, &flags);
 	on_rq = p->on_rq;
 	running = task_current(rq, p);

Index: tip/kernel/sched/features.h
===================================================================

--- tip.orig/kernel/sched/features.h
+++ tip/kernel/sched/features.h

@@ -63,7 +63,10 @@ SCHED_FEAT(RT_RUNTIME_SHARE, true)
 SCHED_FEAT(LB_MIN, false)
 
 #ifdef CONFIG_SCHED_NUMA
+/* Do the working set probing faults: */
 SCHED_FEAT(NUMA,           true)
+/* Do actual migration/placement based on the working set information: */
+SCHED_FEAT(NUMA_MIGRATION, true)
 SCHED_FEAT(NUMA_HOT,       true)
 SCHED_FEAT(NUMA_TTWU_BIAS, false)
 SCHED_FEAT(NUMA_TTWU_TO,   false)


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