linux-kernel - Re: [PATCH V2] cpufreq: stats: Use local

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Date:   Tue, 17 Nov 2020 17:59:42 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Lukasz Luba <lukasz.luba@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] cpufreq: stats: Use local_clock() instead of jiffies

On Tue, Nov 17, 2020 at 12:32 PM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>
> local_clock() has better precision and accuracy as compared to jiffies,
> lets use it for time management in cpufreq stats.
>
> Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> ---
> V2:
> - Doesn't change the units to msec and use local_clock() instead of
>   ktime.
>
>  drivers/cpufreq/cpufreq_stats.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/cpufreq/cpufreq_stats.c b/drivers/cpufreq/cpufreq_stats.c
> index 6cd5c8ab5d49..da717f7cd9a9 100644
> --- a/drivers/cpufreq/cpufreq_stats.c
> +++ b/drivers/cpufreq/cpufreq_stats.c
> @@ -9,9 +9,9 @@
>  #include <linux/cpu.h>
>  #include <linux/cpufreq.h>
>  #include <linux/module.h>
> +#include <linux/sched/clock.h>
>  #include <linux/slab.h>
>
> -
>  struct cpufreq_stats {
>         unsigned int total_trans;
>         unsigned long long last_time;
> @@ -30,7 +30,7 @@ struct cpufreq_stats {
>  static void cpufreq_stats_update(struct cpufreq_stats *stats,
>                                  unsigned long long time)
>  {
> -       unsigned long long cur_time = get_jiffies_64();
> +       unsigned long long cur_time = local_clock();
>
>         stats->time_in_state[stats->last_index] += cur_time - time;
>         stats->last_time = cur_time;
> @@ -42,7 +42,7 @@ static void cpufreq_stats_reset_table(struct cpufreq_stats *stats)
>
>         memset(stats->time_in_state, 0, count * sizeof(u64));
>         memset(stats->trans_table, 0, count * count * sizeof(int));
> -       stats->last_time = get_jiffies_64();
> +       stats->last_time = local_clock();
>         stats->total_trans = 0;
>
>         /* Adjust for the time elapsed since reset was requested */
> @@ -82,18 +82,18 @@ static ssize_t show_time_in_state(struct cpufreq_policy *policy, char *buf)
>                                  * before the reset_pending read above.
>                                  */
>                                 smp_rmb();
> -                               time = get_jiffies_64() - READ_ONCE(stats->reset_time);
> +                               time = local_clock() - READ_ONCE(stats->reset_time);
>                         } else {
>                                 time = 0;
>                         }
>                 } else {
>                         time = stats->time_in_state[i];
>                         if (i == stats->last_index)
> -                               time += get_jiffies_64() - stats->last_time;
> +                               time += local_clock() - stats->last_time;
>                 }
>
>                 len += sprintf(buf + len, "%u %llu\n", stats->freq_table[i],
> -                              jiffies_64_to_clock_t(time));
> +                              nsec_to_clock_t(time));
>         }
>         return len;
>  }
> @@ -109,7 +109,7 @@ static ssize_t store_reset(struct cpufreq_policy *policy, const char *buf,
>          * Defer resetting of stats to cpufreq_stats_record_transition() to
>          * avoid races.
>          */
> -       WRITE_ONCE(stats->reset_time, get_jiffies_64());
> +       WRITE_ONCE(stats->reset_time, local_clock());
>         /*
>          * The memory barrier below is to prevent the readers of reset_time from
>          * seeing a stale or partially updated value.
> @@ -249,7 +249,7 @@ void cpufreq_stats_create_table(struct cpufreq_policy *policy)
>                         stats->freq_table[i++] = pos->frequency;
>
>         stats->state_num = i;
> -       stats->last_time = get_jiffies_64();
> +       stats->last_time = local_clock();
>         stats->last_index = freq_table_get_index(stats, policy->cur);
>
>         policy->stats = stats;
> --

Applied as 5.11 material, thanks!