Commit b9965449 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

tick: Get rid of tick_period 



The variable tick_period is initialized to NSEC_PER_TICK / HZ during boot
and never updated again.

If NSEC_PER_TICK is not an integer multiple of HZ this computation is less
accurate than TICK_NSEC which has proper rounding in place.

Aside of the inaccuracy there is no reason for having this variable at
all. It's just a pointless indirection and all usage sites can just use the
TICK_NSEC constant.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201117132006.766643526@linutronix.de
parent 896b969e

kernel/time/tick-broadcast.c

+1 −1
Original line number Diff line number Diff line
@@ -331,7 +331,7 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev) 
	bc_local = tick_do_periodic_broadcast();



	if (clockevent_state_oneshot(dev)) {

		ktime_t next = ktime_add(dev->next_event, tick_period);

		ktime_t next = ktime_add_ns(dev->next_event, TICK_NSEC);



		clockevents_program_event(dev, next, true);

	}

kernel/time/tick-common.c

+3 −5
Original line number Diff line number Diff line
@@ -32,7 +32,6 @@ DEFINE_PER_CPU(struct tick_device, tick_cpu_device); 
 * no requirement to write hold the jiffies seqcount for it.

 */

ktime_t tick_next_period;

ktime_t tick_period;



/*

 * tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
@@ -90,7 +89,7 @@ static void tick_periodic(int cpu) 
		write_seqcount_begin(&jiffies_seq);



		/* Keep track of the next tick event */

		tick_next_period = ktime_add(tick_next_period, tick_period);

		tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);



		do_timer(1);

		write_seqcount_end(&jiffies_seq);
@@ -129,7 +128,7 @@ void tick_handle_periodic(struct clock_event_device *dev) 
		 * Setup the next period for devices, which do not have

		 * periodic mode:

		 */

		next = ktime_add(next, tick_period);

		next = ktime_add_ns(next, TICK_NSEC);



		if (!clockevents_program_event(dev, next, false))

			return;
@@ -175,7 +174,7 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast) 
		for (;;) {

			if (!clockevents_program_event(dev, next, false))

				return;

			next = ktime_add(next, tick_period);

			next = ktime_add_ns(next, TICK_NSEC);

		}

	}

}
@@ -222,7 +221,6 @@ static void tick_setup_device(struct tick_device *td, 
			tick_do_timer_cpu = cpu;



			tick_next_period = ktime_get();

			tick_period = NSEC_PER_SEC / HZ;

#ifdef CONFIG_NO_HZ_FULL

			/*

			 * The boot CPU may be nohz_full, in which case set

kernel/time/tick-internal.h

+0 −1
Original line number Diff line number Diff line
@@ -15,7 +15,6 @@ 


DECLARE_PER_CPU(struct tick_device, tick_cpu_device);

extern ktime_t tick_next_period;

extern ktime_t tick_period;

extern int tick_do_timer_cpu __read_mostly;



extern void tick_setup_periodic(struct clock_event_device *dev, int broadcast);

kernel/time/tick-sched.c

+11 −11
Original line number Diff line number Diff line
@@ -95,17 +95,17 @@ static void tick_do_update_jiffies64(ktime_t now) 
	write_seqcount_begin(&jiffies_seq);



	delta = ktime_sub(now, tick_next_period);

	if (unlikely(delta >= tick_period)) {

	if (unlikely(delta >= TICK_NSEC)) {

		/* Slow path for long idle sleep times */

		s64 incr = ktime_to_ns(tick_period);

		s64 incr = TICK_NSEC;



		ticks += ktime_divns(delta, incr);



		last_jiffies_update = ktime_add_ns(last_jiffies_update,

						   incr * ticks);

	} else {

		last_jiffies_update = ktime_add(last_jiffies_update,

						tick_period);

		last_jiffies_update = ktime_add_ns(last_jiffies_update,

						   TICK_NSEC);

	}



	/* Advance jiffies to complete the jiffies_seq protected job */
@@ -116,7 +116,7 @@ static void tick_do_update_jiffies64(ktime_t now) 
	 * pairs with the READ_ONCE() in the lockless quick check above.

	 */

	WRITE_ONCE(tick_next_period,

		   ktime_add(last_jiffies_update, tick_period));

		   ktime_add_ns(last_jiffies_update, TICK_NSEC));



	/*

	 * Release the sequence count. calc_global_load() below is not
@@ -691,7 +691,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) 
	hrtimer_set_expires(&ts->sched_timer, ts->last_tick);



	/* Forward the time to expire in the future */

	hrtimer_forward(&ts->sched_timer, now, tick_period);

	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);



	if (ts->nohz_mode == NOHZ_MODE_HIGHRES) {

		hrtimer_start_expires(&ts->sched_timer,
@@ -1260,7 +1260,7 @@ static void tick_nohz_handler(struct clock_event_device *dev) 
	if (unlikely(ts->tick_stopped))

		return;



	hrtimer_forward(&ts->sched_timer, now, tick_period);

	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);

	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);

}
@@ -1297,7 +1297,7 @@ static void tick_nohz_switch_to_nohz(void) 
	next = tick_init_jiffy_update();



	hrtimer_set_expires(&ts->sched_timer, next);

	hrtimer_forward_now(&ts->sched_timer, tick_period);

	hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);

	tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);

	tick_nohz_activate(ts, NOHZ_MODE_LOWRES);

}
@@ -1363,7 +1363,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) 
	if (unlikely(ts->tick_stopped))

		return HRTIMER_NORESTART;



	hrtimer_forward(timer, now, tick_period);

	hrtimer_forward(timer, now, TICK_NSEC);



	return HRTIMER_RESTART;

}
@@ -1397,13 +1397,13 @@ void tick_setup_sched_timer(void) 


	/* Offset the tick to avert jiffies_lock contention. */

	if (sched_skew_tick) {

		u64 offset = ktime_to_ns(tick_period) >> 1;

		u64 offset = TICK_NSEC >> 1;

		do_div(offset, num_possible_cpus());

		offset *= smp_processor_id();

		hrtimer_add_expires_ns(&ts->sched_timer, offset);

	}



	hrtimer_forward(&ts->sched_timer, now, tick_period);

	hrtimer_forward(&ts->sched_timer, now, TICK_NSEC);

	hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);

	tick_nohz_activate(ts, NOHZ_MODE_HIGHRES);

}

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