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SubjectRe: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO
On Thu, Jul 12, 2018 at 01:29:40PM -0400, Johannes Weiner wrote:
> diff --git a/include/linux/sched/stat.h b/include/linux/sched/stat.h
> index 04f1321d14c4..ac39435d1521 100644
> --- a/include/linux/sched/stat.h
> +++ b/include/linux/sched/stat.h
> @@ -28,10 +28,14 @@ static inline int sched_info_on(void)
> return 1;
> #elif defined(CONFIG_TASK_DELAY_ACCT)
> extern int delayacct_on;
> - return delayacct_on;
> -#else
> - return 0;
> + if (delayacct_on)
> + return 1;
> +#elif defined(CONFIG_PSI)
> + extern int psi_disabled;
> + if (!psi_disabled)
> + return 1;
> #endif
> + return 0;
> }
>
> #ifdef CONFIG_SCHEDSTATS

> diff --git a/init/Kconfig b/init/Kconfig
> index 18b151f0ddc1..e34859bda33e 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -457,6 +457,22 @@ config TASK_IO_ACCOUNTING
>
> Say N if unsure.
>
> +config PSI
> + bool "Pressure stall information tracking"
> + select SCHED_INFO

What's the deal here? AFAICT it does not in fact use SCHED_INFO for
_anything_. You just hooked into the sched_info_{en,de}queue() hooks,
but you don't use any of the sched_info data.

So the dependency is an artificial one that should not exist.

> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9586a8141f16..16e8c8c8f432 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -744,7 +744,7 @@ static inline void enqueue_task(struct rq *rq, struct task_struct *p, int flags)
> update_rq_clock(rq);
>
> if (!(flags & ENQUEUE_RESTORE))
> - sched_info_queued(rq, p);
> + sched_info_queued(rq, p, flags & ENQUEUE_WAKEUP);
>
> p->sched_class->enqueue_task(rq, p, flags);
> }
> @@ -755,7 +755,7 @@ static inline void dequeue_task(struct rq *rq, struct task_struct *p, int flags)
> update_rq_clock(rq);
>
> if (!(flags & DEQUEUE_SAVE))
> - sched_info_dequeued(rq, p);
> + sched_info_dequeued(rq, p, flags & DEQUEUE_SLEEP);
>
> p->sched_class->dequeue_task(rq, p, flags);
> }

> diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
> index 8aea199a39b4..15b858cbbcb0 100644
> --- a/kernel/sched/stats.h
> +++ b/kernel/sched/stats.h

> #ifdef CONFIG_SCHED_INFO
> static inline void sched_info_reset_dequeued(struct task_struct *t)
> {
> t->sched_info.last_queued = 0;
> }
>
> +static inline void sched_info_reset_queued(struct task_struct *t, u64 now)
> +{
> + if (!t->sched_info.last_queued)
> + t->sched_info.last_queued = now;
> +}
> +
> /*
> * We are interested in knowing how long it was from the *first* time a
> * task was queued to the time that it finally hit a CPU, we call this routine
> * from dequeue_task() to account for possible rq->clock skew across CPUs. The
> * delta taken on each CPU would annul the skew.
> */
> -static inline void sched_info_dequeued(struct rq *rq, struct task_struct *t)
> +static inline void sched_info_dequeued(struct rq *rq, struct task_struct *t,
> + bool sleep)
> {
> unsigned long long now = rq_clock(rq), delta = 0;
>
> - if (unlikely(sched_info_on()))
> + if (unlikely(sched_info_on())) {
> if (t->sched_info.last_queued)
> delta = now - t->sched_info.last_queued;
> + psi_dequeue(t, now, sleep);
> + }
> sched_info_reset_dequeued(t);
> t->sched_info.run_delay += delta;
>
> @@ -104,11 +190,14 @@ static void sched_info_arrive(struct rq *rq, struct task_struct *t)
> * the timestamp if it is already not set. It's assumed that
> * sched_info_dequeued() will clear that stamp when appropriate.
> */
> -static inline void sched_info_queued(struct rq *rq, struct task_struct *t)
> +static inline void sched_info_queued(struct rq *rq, struct task_struct *t,
> + bool wakeup)
> {
> if (unlikely(sched_info_on())) {
> - if (!t->sched_info.last_queued)
> - t->sched_info.last_queued = rq_clock(rq);
> + unsigned long long now = rq_clock(rq);
> +
> + sched_info_reset_queued(t, now);
> + psi_enqueue(t, now, wakeup);
> }
> }
>
> @@ -127,7 +216,8 @@ static inline void sched_info_depart(struct rq *rq, struct task_struct *t)
> rq_sched_info_depart(rq, delta);
>
> if (t->state == TASK_RUNNING)
> - sched_info_queued(rq, t);
> + if (unlikely(sched_info_on()))
> + sched_info_reset_queued(t, rq_clock(rq));
> }

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