2020-10-09 17:37:39

by jun qian

Subject: [PATCH 1/1] Sched/fair: Improve the accuracy of sched_stat_wait statistics

From: jun qian <[email protected]>

When the sched_schedstat changes from 0 to 1, some sched se maybe
already in the runqueue, the se->statistics.wait_start will be 0.
So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
wrong. We need to avoid this scenario.

Signed-off-by: jun qian <[email protected]>
Signed-off-by: Yafang Shao <[email protected]>
---
kernel/sched/fair.c | 9 +++++++++
1 file changed, 9 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1a68a05..6f8ca0c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -906,6 +906,15 @@ static void update_curr_fair(struct rq *rq)
if (!schedstat_enabled())
return;

+ /*
+ * When the sched_schedstat changes from 0 to 1, some sched se
+ * maybe already in the runqueue, the se->statistics.wait_start
+ * will be 0.So it will let the delta wrong. We need to avoid this
+ * scenario.
+ */
+ if (unlikely(!schedstat_val(se->statistics.wait_start)))
+ return;
+
delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);

if (entity_is_task(se)) {
--
1.8.3.1

2020-10-14 16:34:40

by Peter Zijlstra

Subject: Re: [PATCH 1/1] Sched/fair: Improve the accuracy of sched_stat_wait statistics

On Fri, Oct 09, 2020 at 05:25:30PM +0800, [email protected] wrote:
> From: jun qian <[email protected]>
>
> When the sched_schedstat changes from 0 to 1, some sched se maybe
> already in the runqueue, the se->statistics.wait_start will be 0.
> So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> wrong. We need to avoid this scenario.
>
> Signed-off-by: jun qian <[email protected]>
> Signed-off-by: Yafang Shao <[email protected]>

This SoB chain isn't valid. Did Yafang's tag need to a reviewed-by or
something?

> ---
> kernel/sched/fair.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1a68a05..6f8ca0c 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -906,6 +906,15 @@ static void update_curr_fair(struct rq *rq)
> if (!schedstat_enabled())
> return;
>
> + /*
> + * When the sched_schedstat changes from 0 to 1, some sched se
> + * maybe already in the runqueue, the se->statistics.wait_start
> + * will be 0.So it will let the delta wrong. We need to avoid this
> + * scenario.
> + */
> + if (unlikely(!schedstat_val(se->statistics.wait_start)))
> + return;
> +
> delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
>
> if (entity_is_task(se)) {
> --
> 1.8.3.1
>

2020-10-15 17:27:51

by Yafang Shao

Subject: Re: [PATCH 1/1] Sched/fair: Improve the accuracy of sched_stat_wait statistics

On Wed, Oct 14, 2020 at 9:19 PM Peter Zijlstra <[email protected]> wrote:
>
> On Fri, Oct 09, 2020 at 05:25:30PM +0800, [email protected] wrote:
> > From: jun qian <[email protected]>
> >
> > When the sched_schedstat changes from 0 to 1, some sched se maybe
> > already in the runqueue, the se->statistics.wait_start will be 0.
> > So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
> > wrong. We need to avoid this scenario.
> >
> > Signed-off-by: jun qian <[email protected]>
> > Signed-off-by: Yafang Shao <[email protected]>
>
> This SoB chain isn't valid. Did Yafang's tag need to a reviewed-by or
> something?
>

This patch improves the behavior when sched_schedstat is changed from
0 to 1, so it looks good to me.

Reviewed-by: Yafang Shao <[email protected]>

> > ---
> > kernel/sched/fair.c | 9 +++++++++
> > 1 file changed, 9 insertions(+)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 1a68a05..6f8ca0c 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -906,6 +906,15 @@ static void update_curr_fair(struct rq *rq)
> > if (!schedstat_enabled())
> > return;
> >
> > + /*
> > + * When the sched_schedstat changes from 0 to 1, some sched se
> > + * maybe already in the runqueue, the se->statistics.wait_start
> > + * will be 0.So it will let the delta wrong. We need to avoid this
> > + * scenario.
> > + */
> > + if (unlikely(!schedstat_val(se->statistics.wait_start)))
> > + return;
> > +
> > delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
> >
> > if (entity_is_task(se)) {
> > --
> > 1.8.3.1
> >



--
Thanks
Yafang