[RFC patch v3 20/20] sched: Introduce SCHED_CACHE_WAKE to control LLC aggregation on wake up

[Tim Chen]

Introduce SCHED_CACHE_WAKE feature to enable or disable cache-aware
wake up. Disable this feature by default because cache-aware wakeup
is overly aggressive in stacking wakees of the same process on the same LLC,
if they are frequently woken up.

The wake ups can be much more frequent than load balances, adding
much overhead when load balance alone for LLC aggregation is sufficient.

Co-developed-by: Chen Yu <yu.c.chen@xxxxxxxxx>
Signed-off-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
---
 kernel/sched/fair.c     | 6 +++++-
 kernel/sched/features.h | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index af742601f2d7..32c90fab0d63 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9028,7 +9028,7 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	struct mm_struct *mm = p->mm;
 	int cpu;
 
-	if (!sched_feat(SCHED_CACHE))
+	if (!sched_feat(SCHED_CACHE) || !sched_feat(SCHED_CACHE_WAKE))
 		return prev_cpu;
 
 	if (!mm || p->nr_cpus_allowed == 1)
@@ -9041,6 +9041,10 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	if (cpus_share_cache(cpu, prev_cpu))
 		return prev_cpu;
 
+	if (_get_migrate_hint(prev_cpu, cpu,
+			      task_util(p), true) == mig_forbid)
+		return prev_cpu;
+
 	if (static_branch_likely(&sched_numa_balancing) &&
 	    __migrate_degrades_locality(p, prev_cpu, cpu, false) > 0) {
 		/*
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 11dbd74cd365..44b408cf0dd4 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -89,6 +89,7 @@ SCHED_FEAT(SIS_UTIL, true)
 
 SCHED_FEAT(SCHED_CACHE, true)
 SCHED_FEAT(SCHED_CACHE_LB, true)
+SCHED_FEAT(SCHED_CACHE_WAKE, false)
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls
  * in a single rq->lock section. Default disabled because the
-- 
2.32.0