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Message-ID: <CAJuCfpGJBYSahyDGpPTJoMOSN-U4mXvpgoGnj8k2UV0WGyB_pg@mail.gmail.com>
Date: Mon, 20 Mar 2023 14:06:11 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Domenico Cerasuolo <cerasuolodomenico@...il.com>
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
brauner@...nel.org, chris@...isdown.name, hannes@...xchg.org
Subject: Re: [PATCH 1/4] sched/psi: rearrange polling code in preparation
On Thu, Mar 9, 2023 at 9:08 AM Domenico Cerasuolo
<cerasuolodomenico@...il.com> wrote:
>
> Move a few functions up in the file to avoid forward declaration needed
> in the patch implementing unprivileged PSI triggers.
>
> Suggested-by: Johannes Weiner <hannes@...xchg.org>
> Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@...il.com>
LGTM. Will Ack when we finalize the rest of the patchset.
> ---
> kernel/sched/psi.c | 196 ++++++++++++++++++++++-----------------------
> 1 file changed, 98 insertions(+), 98 deletions(-)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 02e011cabe91..fe9269f1d2a4 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -384,92 +384,6 @@ static void collect_percpu_times(struct psi_group *group,
> *pchanged_states = changed_states;
> }
>
> -static u64 update_averages(struct psi_group *group, u64 now)
> -{
> - unsigned long missed_periods = 0;
> - u64 expires, period;
> - u64 avg_next_update;
> - int s;
> -
> - /* avgX= */
> - expires = group->avg_next_update;
> - if (now - expires >= psi_period)
> - missed_periods = div_u64(now - expires, psi_period);
> -
> - /*
> - * The periodic clock tick can get delayed for various
> - * reasons, especially on loaded systems. To avoid clock
> - * drift, we schedule the clock in fixed psi_period intervals.
> - * But the deltas we sample out of the per-cpu buckets above
> - * are based on the actual time elapsing between clock ticks.
> - */
> - avg_next_update = expires + ((1 + missed_periods) * psi_period);
> - period = now - (group->avg_last_update + (missed_periods * psi_period));
> - group->avg_last_update = now;
> -
> - for (s = 0; s < NR_PSI_STATES - 1; s++) {
> - u32 sample;
> -
> - sample = group->total[PSI_AVGS][s] - group->avg_total[s];
> - /*
> - * Due to the lockless sampling of the time buckets,
> - * recorded time deltas can slip into the next period,
> - * which under full pressure can result in samples in
> - * excess of the period length.
> - *
> - * We don't want to report non-sensical pressures in
> - * excess of 100%, nor do we want to drop such events
> - * on the floor. Instead we punt any overage into the
> - * future until pressure subsides. By doing this we
> - * don't underreport the occurring pressure curve, we
> - * just report it delayed by one period length.
> - *
> - * The error isn't cumulative. As soon as another
> - * delta slips from a period P to P+1, by definition
> - * it frees up its time T in P.
> - */
> - if (sample > period)
> - sample = period;
> - group->avg_total[s] += sample;
> - calc_avgs(group->avg[s], missed_periods, sample, period);
> - }
> -
> - return avg_next_update;
> -}
> -
> -static void psi_avgs_work(struct work_struct *work)
> -{
> - struct delayed_work *dwork;
> - struct psi_group *group;
> - u32 changed_states;
> - u64 now;
> -
> - dwork = to_delayed_work(work);
> - group = container_of(dwork, struct psi_group, avgs_work);
> -
> - mutex_lock(&group->avgs_lock);
> -
> - now = sched_clock();
> -
> - collect_percpu_times(group, PSI_AVGS, &changed_states);
> - /*
> - * If there is task activity, periodically fold the per-cpu
> - * times and feed samples into the running averages. If things
> - * are idle and there is no data to process, stop the clock.
> - * Once restarted, we'll catch up the running averages in one
> - * go - see calc_avgs() and missed_periods.
> - */
> - if (now >= group->avg_next_update)
> - group->avg_next_update = update_averages(group, now);
> -
> - if (changed_states & PSI_STATE_RESCHEDULE) {
> - schedule_delayed_work(dwork, nsecs_to_jiffies(
> - group->avg_next_update - now) + 1);
> - }
> -
> - mutex_unlock(&group->avgs_lock);
> -}
> -
> /* Trigger tracking window manipulations */
> static void window_reset(struct psi_window *win, u64 now, u64 value,
> u64 prev_growth)
> @@ -516,18 +430,6 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
> return growth;
> }
>
> -static void init_triggers(struct psi_group *group, u64 now)
> -{
> - struct psi_trigger *t;
> -
> - list_for_each_entry(t, &group->triggers, node)
> - window_reset(&t->win, now,
> - group->total[PSI_POLL][t->state], 0);
> - memcpy(group->polling_total, group->total[PSI_POLL],
> - sizeof(group->polling_total));
> - group->polling_next_update = now + group->poll_min_period;
> -}
> -
> static u64 update_triggers(struct psi_group *group, u64 now)
> {
> struct psi_trigger *t;
> @@ -590,6 +492,104 @@ static u64 update_triggers(struct psi_group *group, u64 now)
> return now + group->poll_min_period;
> }
>
> +static u64 update_averages(struct psi_group *group, u64 now)
> +{
> + unsigned long missed_periods = 0;
> + u64 expires, period;
> + u64 avg_next_update;
> + int s;
> +
> + /* avgX= */
> + expires = group->avg_next_update;
> + if (now - expires >= psi_period)
> + missed_periods = div_u64(now - expires, psi_period);
> +
> + /*
> + * The periodic clock tick can get delayed for various
> + * reasons, especially on loaded systems. To avoid clock
> + * drift, we schedule the clock in fixed psi_period intervals.
> + * But the deltas we sample out of the per-cpu buckets above
> + * are based on the actual time elapsing between clock ticks.
> + */
> + avg_next_update = expires + ((1 + missed_periods) * psi_period);
> + period = now - (group->avg_last_update + (missed_periods * psi_period));
> + group->avg_last_update = now;
> +
> + for (s = 0; s < NR_PSI_STATES - 1; s++) {
> + u32 sample;
> +
> + sample = group->total[PSI_AVGS][s] - group->avg_total[s];
> + /*
> + * Due to the lockless sampling of the time buckets,
> + * recorded time deltas can slip into the next period,
> + * which under full pressure can result in samples in
> + * excess of the period length.
> + *
> + * We don't want to report non-sensical pressures in
> + * excess of 100%, nor do we want to drop such events
> + * on the floor. Instead we punt any overage into the
> + * future until pressure subsides. By doing this we
> + * don't underreport the occurring pressure curve, we
> + * just report it delayed by one period length.
> + *
> + * The error isn't cumulative. As soon as another
> + * delta slips from a period P to P+1, by definition
> + * it frees up its time T in P.
> + */
> + if (sample > period)
> + sample = period;
> + group->avg_total[s] += sample;
> + calc_avgs(group->avg[s], missed_periods, sample, period);
> + }
> +
> + return avg_next_update;
> +}
> +
> +static void psi_avgs_work(struct work_struct *work)
> +{
> + struct delayed_work *dwork;
> + struct psi_group *group;
> + u32 changed_states;
> + u64 now;
> +
> + dwork = to_delayed_work(work);
> + group = container_of(dwork, struct psi_group, avgs_work);
> +
> + mutex_lock(&group->avgs_lock);
> +
> + now = sched_clock();
> +
> + collect_percpu_times(group, PSI_AVGS, &changed_states);
> + /*
> + * If there is task activity, periodically fold the per-cpu
> + * times and feed samples into the running averages. If things
> + * are idle and there is no data to process, stop the clock.
> + * Once restarted, we'll catch up the running averages in one
> + * go - see calc_avgs() and missed_periods.
> + */
> + if (now >= group->avg_next_update)
> + group->avg_next_update = update_averages(group, now);
> +
> + if (changed_states & PSI_STATE_RESCHEDULE) {
> + schedule_delayed_work(dwork, nsecs_to_jiffies(
> + group->avg_next_update - now) + 1);
> + }
> +
> + mutex_unlock(&group->avgs_lock);
> +}
> +
> +static void init_triggers(struct psi_group *group, u64 now)
> +{
> + struct psi_trigger *t;
> +
> + list_for_each_entry(t, &group->triggers, node)
> + window_reset(&t->win, now,
> + group->total[PSI_POLL][t->state], 0);
> + memcpy(group->polling_total, group->total[PSI_POLL],
> + sizeof(group->polling_total));
> + group->polling_next_update = now + group->poll_min_period;
> +}
> +
> /* Schedule polling if it's not already scheduled or forced. */
> static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay,
> bool force)
> --
> 2.34.1
>
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