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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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