Re: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO

[Peter Zijlstra]

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));
>  }