[RFC PATCH 9/9] sched: rotate the cpu search window for better spread

From: subhra mazumdar
Date: Fri Aug 30 2019 - 13:55:58 EST


Rotate the cpu search window for better spread of threads. This will ensure
an idle cpu will quickly be found if one exists.

Signed-off-by: subhra mazumdar <subhra.mazumdar@xxxxxxxxxx>
---
kernel/sched/fair.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 94dd4a32..7419b47 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6188,7 +6188,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
u64 avg_cost, avg_idle;
u64 time, cost;
s64 delta;
- int cpu, floor, nr = INT_MAX;
+ int cpu, floor, target_tmp, nr = INT_MAX;

this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
if (!this_sd)
@@ -6213,9 +6213,15 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
nr = floor;
}

+ if (per_cpu(next_cpu, target) != -1)
+ target_tmp = per_cpu(next_cpu, target);
+ else
+ target_tmp = target;
+
time = local_clock();

- for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
+ for_each_cpu_wrap(cpu, sched_domain_span(sd), target_tmp) {
+ per_cpu(next_cpu, target) = cpu;
if (!--nr)
return -1;
if (!cpumask_test_cpu(cpu, &p->cpus_allowed))
--
2.9.3