2019-08-30 17:58:42

by Subhra Mazumdar

Subject: [RFC PATCH 4/9] sched: SIS_CORE to disable idle core search

Use SIS_CORE to disable idle core search. For some workloads
select_idle_core becomes a scalability bottleneck, removing it improves
throughput. Also there are workloads where disabling it can hurt latency,
so need to have an option.

Signed-off-by: subhra mazumdar <[email protected]>
---
kernel/sched/fair.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c31082d..23ec9c6 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6268,9 +6268,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
if (!sd)
return target;

- i = select_idle_core(p, sd, target);
- if ((unsigned)i < nr_cpumask_bits)
- return i;
+ if (sched_feat(SIS_CORE)) {
+ i = select_idle_core(p, sd, target);
+ if ((unsigned)i < nr_cpumask_bits)
+ return i;
+ }

i = select_idle_cpu(p, sd, target);
if ((unsigned)i < nr_cpumask_bits)
--
2.9.3

2019-09-05 12:28:08

by Patrick Bellasi

Subject: Re: [RFC PATCH 4/9] sched: SIS_CORE to disable idle core search

On Fri, Aug 30, 2019 at 18:49:39 +0100, subhra mazumdar wrote...

> Use SIS_CORE to disable idle core search. For some workloads
> select_idle_core becomes a scalability bottleneck, removing it improves
> throughput. Also there are workloads where disabling it can hurt latency,
> so need to have an option.
>
> Signed-off-by: subhra mazumdar <[email protected]>
> ---
> kernel/sched/fair.c | 8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c31082d..23ec9c6 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6268,9 +6268,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
> if (!sd)
> return target;
>
> - i = select_idle_core(p, sd, target);
> - if ((unsigned)i < nr_cpumask_bits)
> - return i;
> + if (sched_feat(SIS_CORE)) {
> + i = select_idle_core(p, sd, target);
> + if ((unsigned)i < nr_cpumask_bits)
> + return i;
> + }
>
> i = select_idle_cpu(p, sd, target);
> if ((unsigned)i < nr_cpumask_bits)

This looks like should be squashed with the previous one, or whatever
code you'll add to define when this "biasing" is to be used or not.

Best,
Patrick

--
#include <best/regards.h>

Patrick Bellasi