[RFC PATCH v4 03/28] sched: Avoid task migration within its preferred LLC

[Chen Yu]

It was found that when running schbench, there is a
significant amount of in-LLC task migrations, even if
the wakee is woken up on its preferred LLC. This
leads to core-to-core latency and impairs performance.

Inhibit task migration if the wakee is already in its
preferred LLC.

Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e97ab46509e3..00bd0d25bc91 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8835,6 +8835,8 @@ static int select_cache_cpu(struct task_struct *p, int prev_cpu)
 	if (cpu < 0)
 		return prev_cpu;
 
+	if (cpus_share_cache(cpu, prev_cpu))
+		return prev_cpu;
 
 	if (static_branch_likely(&sched_numa_balancing) &&
 	    __migrate_degrades_locality(p, prev_cpu, cpu, false) > 0) {
-- 
2.25.1