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    Subject[PATCH v2] psi: Remove the redundant psi_task_tick
    Date
    When the current task in a cgroup is in_memstall, the corresponding groupc
    on that cpu is in PSI_MEM_FULL state, so we can exploit that to remove the
    redundant psi_task_tick from scheduler_tick to save this periodic cost.

    Signed-off-by: Muchun Song <songmuchun@bytedance.com>
    Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
    ---
    include/linux/psi.h | 1 -
    kernel/sched/core.c | 1 -
    kernel/sched/psi.c | 49 ++++++++++++++-----------------------------------
    kernel/sched/stats.h | 9 ---------
    4 files changed, 14 insertions(+), 46 deletions(-)

    diff --git a/include/linux/psi.h b/include/linux/psi.h
    index 7361023f3fdd..65eb1476ac70 100644
    --- a/include/linux/psi.h
    +++ b/include/linux/psi.h
    @@ -20,7 +20,6 @@ void psi_task_change(struct task_struct *task, int clear, int set);
    void psi_task_switch(struct task_struct *prev, struct task_struct *next,
    bool sleep);

    -void psi_memstall_tick(struct task_struct *task, int cpu);
    void psi_memstall_enter(unsigned long *flags);
    void psi_memstall_leave(unsigned long *flags);

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 15d2562118d1..31788a9b335b 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -4533,7 +4533,6 @@ void scheduler_tick(void)
    update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
    curr->sched_class->task_tick(rq, curr, 0);
    calc_global_load_tick(rq);
    - psi_task_tick(rq);

    rq_unlock(rq, &rf);

    diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
    index 2293c45d289d..6e46d9eb279b 100644
    --- a/kernel/sched/psi.c
    +++ b/kernel/sched/psi.c
    @@ -644,8 +644,7 @@ static void poll_timer_fn(struct timer_list *t)
    wake_up_interruptible(&group->poll_wait);
    }

    -static void record_times(struct psi_group_cpu *groupc, int cpu,
    - bool memstall_tick)
    +static void record_times(struct psi_group_cpu *groupc, int cpu)
    {
    u32 delta;
    u64 now;
    @@ -664,23 +663,6 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
    groupc->times[PSI_MEM_SOME] += delta;
    if (groupc->state_mask & (1 << PSI_MEM_FULL))
    groupc->times[PSI_MEM_FULL] += delta;
    - else if (memstall_tick) {
    - u32 sample;
    - /*
    - * Since we care about lost potential, a
    - * memstall is FULL when there are no other
    - * working tasks, but also when the CPU is
    - * actively reclaiming and nothing productive
    - * could run even if it were runnable.
    - *
    - * When the timer tick sees a reclaiming CPU,
    - * regardless of runnable tasks, sample a FULL
    - * tick (or less if it hasn't been a full tick
    - * since the last state change).
    - */
    - sample = min(delta, (u32)jiffies_to_nsecs(1));
    - groupc->times[PSI_MEM_FULL] += sample;
    - }
    }

    if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
    @@ -714,7 +696,7 @@ static void psi_group_change(struct psi_group *group, int cpu,
    */
    write_seqcount_begin(&groupc->seq);

    - record_times(groupc, cpu, false);
    + record_times(groupc, cpu);

    for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
    if (!(m & (1 << t)))
    @@ -738,6 +720,18 @@ static void psi_group_change(struct psi_group *group, int cpu,
    if (test_state(groupc->tasks, s))
    state_mask |= (1 << s);
    }
    +
    + /*
    + * Since we care about lost potential, a memstall is FULL
    + * when there are no other working tasks, but also when
    + * the CPU is actively reclaiming and nothing productive
    + * could run even if it were runnable. So when the current
    + * task in a cgroup is in_memstall, the corresponding groupc
    + * on that cpu is in PSI_MEM_FULL state.
    + */
    + if (groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)
    + state_mask |= (1 << PSI_MEM_FULL);
    +
    groupc->state_mask = state_mask;

    write_seqcount_end(&groupc->seq);
    @@ -859,21 +853,6 @@ void psi_task_switch(struct task_struct *prev, struct task_struct *next,
    }
    }

    -void psi_memstall_tick(struct task_struct *task, int cpu)
    -{
    - struct psi_group *group;
    - void *iter = NULL;
    -
    - while ((group = iterate_groups(task, &iter))) {
    - struct psi_group_cpu *groupc;
    -
    - groupc = per_cpu_ptr(group->pcpu, cpu);
    - write_seqcount_begin(&groupc->seq);
    - record_times(groupc, cpu, true);
    - write_seqcount_end(&groupc->seq);
    - }
    -}
    -
    /**
    * psi_memstall_enter - mark the beginning of a memory stall section
    * @flags: flags to handle nested sections
    diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
    index 33d0daf83842..9e4e67a94731 100644
    --- a/kernel/sched/stats.h
    +++ b/kernel/sched/stats.h
    @@ -144,14 +144,6 @@ static inline void psi_sched_switch(struct task_struct *prev,
    psi_task_switch(prev, next, sleep);
    }

    -static inline void psi_task_tick(struct rq *rq)
    -{
    - if (static_branch_likely(&psi_disabled))
    - return;
    -
    - if (unlikely(rq->curr->in_memstall))
    - psi_memstall_tick(rq->curr, cpu_of(rq));
    -}
    #else /* CONFIG_PSI */
    static inline void psi_enqueue(struct task_struct *p, bool wakeup) {}
    static inline void psi_dequeue(struct task_struct *p, bool sleep) {}
    @@ -159,7 +151,6 @@ static inline void psi_ttwu_dequeue(struct task_struct *p) {}
    static inline void psi_sched_switch(struct task_struct *prev,
    struct task_struct *next,
    bool sleep) {}
    -static inline void psi_task_tick(struct rq *rq) {}
    #endif /* CONFIG_PSI */

    #ifdef CONFIG_SCHED_INFO
    --
    2.11.0
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