sched_clock_irqtime may be disabled due to the clock source. When disabled,
irq_time_read() won't change over time, so there is nothing to account. We
can save iterating the whole hierarchy on every tick and context switch.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
---
 kernel/sched/psi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 84dad1511d1e..6836c34d063e 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -998,7 +998,7 @@ void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_st
 	s64 delta;
 	u64 irq;
 
-	if (static_branch_likely(&psi_disabled))
+	if (static_branch_likely(&psi_disabled) || !irqtime_enabled())
 		return;
 
 	if (!curr->pid)
@@ -1286,7 +1286,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
 	bool privileged;
 	u32 window_us;
 
-	if (static_branch_likely(&psi_disabled))
+	if (static_branch_likely(&psi_disabled) || !irqtime_enabled())
 		return ERR_PTR(-EOPNOTSUPP);
 
 	/*
-- 
2.43.5

On Wed, Dec 11, 2024 at 09:17:28PM GMT, Yafang Shao <laoar.shao@gmail.com> wrote:
> @@ -1286,7 +1286,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
>  	bool privileged;
>  	u32 window_us;
>  
> -	if (static_branch_likely(&psi_disabled))
> +	if (static_branch_likely(&psi_disabled) || !irqtime_enabled())
>  		return ERR_PTR(-EOPNOTSUPP);

Beware this jumps out for _any_ PSI metric when only irq is disabled.
I meant to add a guard to psi_show() (this is psi_trigger_create()).

Michal

On Wed, Dec 11, 2024 at 9:56 PM Michal Koutný <mkoutny@suse.com> wrote:
>
> On Wed, Dec 11, 2024 at 09:17:28PM GMT, Yafang Shao <laoar.shao@gmail.com> wrote:
> > @@ -1286,7 +1286,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
> >       bool privileged;
> >       u32 window_us;
> >
> > -     if (static_branch_likely(&psi_disabled))
> > +     if (static_branch_likely(&psi_disabled) || !irqtime_enabled())
> >               return ERR_PTR(-EOPNOTSUPP);
>
> Beware this jumps out for _any_ PSI metric when only irq is disabled.
> I meant to add a guard to psi_show() (this is psi_trigger_create()).

My apologies, I'll fix it in the next version. How about the following
change instead?

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 7341d33d9118..263c26a36511 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -1233,6 +1233,9 @@ int psi_show(struct seq_file *m, struct
psi_group *group, enum psi_res res)
        if (static_branch_likely(&psi_disabled))
                return -EOPNOTSUPP;

+       if (!irqtime_enabled() && res == PSI_IRQ)
+               return -EOPNOTSUPP;
+
        /* Update averages before reporting them */
        mutex_lock(&group->avgs_lock);
        now = sched_clock();



--
Regards
Yafang

On Wed, Dec 11, 2024 at 10:07:41PM GMT, Yafang Shao <laoar.shao@gmail.com> wrote:
> My apologies, I'll fix it in the next version. How about the following
> change instead?
> 
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 7341d33d9118..263c26a36511 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -1233,6 +1233,9 @@ int psi_show(struct seq_file *m, struct
> psi_group *group, enum psi_res res)
>         if (static_branch_likely(&psi_disabled))
>                 return -EOPNOTSUPP;
> 
> +       if (!irqtime_enabled() && res == PSI_IRQ)
> +               return -EOPNOTSUPP;
> +
>         /* Update averages before reporting them */
>         mutex_lock(&group->avgs_lock);
>         now = sched_clock();

That looks correct.

Michal