Re: [patch 02/39] hrtimer: Get rid of the resolution field in hrtimer_clock_base

[Frans Klaver <fransklaver@gmail.com>]

On Tue, Apr 14, 2015 at 11:08 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
> The field has no value because all clock bases have the same
> resolution. The resolution only changes when we switch to high
> resolution timer mode. We can evaluate that from a single static
> variable as well. In the !HIGHRES case its simply a constant.
>
> Export the variable, so we can simplify the usage sites.

There seems to be only one usage site outside hrtimer.c itself. That
one only reads the value. Wouldn't it make sense to keep the variable
from the interface and use a read function instead?


> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>  include/linux/hrtimer.h  |    6 ++++--
>  kernel/time/hrtimer.c    |   26 +++++++++-----------------
>  kernel/time/timer_list.c |    8 ++++----
>  3 files changed, 17 insertions(+), 23 deletions(-)
>
> Index: tip/include/linux/hrtimer.h
> ===================================================================
> --- tip.orig/include/linux/hrtimer.h
> +++ tip/include/linux/hrtimer.h
> @@ -137,7 +137,6 @@ struct hrtimer_sleeper {
>   *                     timer to a base on another cpu.
>   * @clockid:           clock id for per_cpu support
>   * @active:            red black tree root node for the active timers
> - * @resolution:                the resolution of the clock, in nanoseconds
>   * @get_time:          function to retrieve the current time of the clock
>   * @softirq_time:      the time when running the hrtimer queue in the softirq
>   * @offset:            offset of this clock to the monotonic base
> @@ -147,7 +146,6 @@ struct hrtimer_clock_base {
>         int                     index;
>         clockid_t               clockid;
>         struct timerqueue_head  active;
> -       ktime_t                 resolution;
>         ktime_t                 (*get_time)(void);
>         ktime_t                 softirq_time;
>         ktime_t                 offset;
> @@ -295,11 +293,15 @@ extern void hrtimer_peek_ahead_timers(vo
>
>  extern void clock_was_set_delayed(void);
>
> +extern unsigned int hrtimer_resolution;
> +
>  #else
>
>  # define MONOTONIC_RES_NSEC    LOW_RES_NSEC
>  # define KTIME_MONOTONIC_RES   KTIME_LOW_RES
>
> +#define hrtimer_resolution     LOW_RES_NSEC
> +
>  static inline void hrtimer_peek_ahead_timers(void) { }
>
>  /*
> Index: tip/kernel/time/hrtimer.c
> ===================================================================
> --- tip.orig/kernel/time/hrtimer.c
> +++ tip/kernel/time/hrtimer.c
> @@ -66,7 +66,6 @@
>   */
>  DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
>  {
> -
>         .lock = __RAW_SPIN_LOCK_UNLOCKED(hrtimer_bases.lock),
>         .clock_base =
>         {
> @@ -74,25 +73,21 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base,
>                         .index = HRTIMER_BASE_MONOTONIC,
>                         .clockid = CLOCK_MONOTONIC,
>                         .get_time = &ktime_get,
> -                       .resolution = KTIME_LOW_RES,
>                 },
>                 {
>                         .index = HRTIMER_BASE_REALTIME,
>                         .clockid = CLOCK_REALTIME,
>                         .get_time = &ktime_get_real,
> -                       .resolution = KTIME_LOW_RES,
>                 },
>                 {
>                         .index = HRTIMER_BASE_BOOTTIME,
>                         .clockid = CLOCK_BOOTTIME,
>                         .get_time = &ktime_get_boottime,
> -                       .resolution = KTIME_LOW_RES,
>                 },
>                 {
>                         .index = HRTIMER_BASE_TAI,
>                         .clockid = CLOCK_TAI,
>                         .get_time = &ktime_get_clocktai,
> -                       .resolution = KTIME_LOW_RES,
>                 },
>         }
>  };
> @@ -478,6 +473,8 @@ static ktime_t __hrtimer_get_next_event(
>   * High resolution timer enabled ?
>   */
>  static int hrtimer_hres_enabled __read_mostly  = 1;
> +unsigned int hrtimer_resolution __read_mostly = LOW_RES_NSEC;
> +EXPORT_SYMBOL_GPL(hrtimer_resolution);
>
>  /*
>   * Enable / Disable high resolution mode
> @@ -660,7 +657,7 @@ static void retrigger_next_event(void *a
>   */
>  static int hrtimer_switch_to_hres(void)
>  {
> -       int i, cpu = smp_processor_id();
> +       int cpu = smp_processor_id();
>         struct hrtimer_cpu_base *base = &per_cpu(hrtimer_bases, cpu);
>         unsigned long flags;
>
> @@ -676,8 +673,7 @@ static int hrtimer_switch_to_hres(void)
>                 return 0;
>         }
>         base->hres_active = 1;
> -       for (i = 0; i < HRTIMER_MAX_CLOCK_BASES; i++)
> -               base->clock_base[i].resolution = KTIME_HIGH_RES;
> +       hrtimer_resolution = HIGH_RES_NSEC;
>
>         tick_setup_sched_timer();
>         /* "Retrigger" the interrupt to get things going */
> @@ -812,8 +808,8 @@ u64 hrtimer_forward(struct hrtimer *time
>         if (delta.tv64 < 0)
>                 return 0;
>
> -       if (interval.tv64 < timer->base->resolution.tv64)
> -               interval.tv64 = timer->base->resolution.tv64;
> +       if (interval.tv64 < hrtimer_resolution)
> +               interval.tv64 = hrtimer_resolution;
>
>         if (unlikely(delta.tv64 >= interval.tv64)) {
>                 s64 incr = ktime_to_ns(interval);
> @@ -955,7 +951,7 @@ int __hrtimer_start_range_ns(struct hrti
>                  * timeouts. This will go away with the GTOD framework.
>                  */
>  #ifdef CONFIG_TIME_LOW_RES
> -               tim = ktime_add_safe(tim, base->resolution);
> +               tim = ktime_add_safe(tim, ktime_set(0, hrtimer_resolution));
>  #endif
>         }
>
> @@ -1185,12 +1181,8 @@ EXPORT_SYMBOL_GPL(hrtimer_init);
>   */
>  int hrtimer_get_res(const clockid_t which_clock, struct timespec *tp)
>  {
> -       struct hrtimer_cpu_base *cpu_base;
> -       int base = hrtimer_clockid_to_base(which_clock);
> -
> -       cpu_base = raw_cpu_ptr(&hrtimer_bases);
> -       *tp = ktime_to_timespec(cpu_base->clock_base[base].resolution);
> -
> +       tp->tv_sec = 0;
> +       tp->tv_nsec = hrtimer_resolution;
>         return 0;
>  }
>  EXPORT_SYMBOL_GPL(hrtimer_get_res);
> Index: tip/kernel/time/timer_list.c
> ===================================================================
> --- tip.orig/kernel/time/timer_list.c
> +++ tip/kernel/time/timer_list.c
> @@ -120,10 +120,10 @@ static void
>  print_base(struct seq_file *m, struct hrtimer_clock_base *base, u64 now)
>  {
>         SEQ_printf(m, "  .base:       %pK\n", base);
> -       SEQ_printf(m, "  .index:      %d\n",
> -                       base->index);
> -       SEQ_printf(m, "  .resolution: %Lu nsecs\n",
> -                       (unsigned long long)ktime_to_ns(base->resolution));
> +       SEQ_printf(m, "  .index:      %d\n", base->index);
> +
> +       SEQ_printf(m, "  .resolution: %u nsecs\n", (unsigned) hrtimer_resolution);

hrtimer_resolution already is an unsigned int. Doesn't that make this
cast pointless?

Thanks,
Frans