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Commit 895bdfa7 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

hrtimer: Keep pointer to first timer and simplify __remove_hrtimer() 



__remove_hrtimer() needs to evaluate the expiry time to figure out
whether the timer which is removed is eventually the first expiring
timer on the cpu. Keep a pointer to it, which is lazily updated, so we
can avoid the evaluation dance and retrieve the information from there.

Generates slightly better code.

Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/20150414203501.752838019@linutronix.de


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent b97f44c9

include/linux/hrtimer.h

+6 −0
Original line number Diff line number Diff line
@@ -172,6 +172,7 @@ enum hrtimer_base_type { 
 * @clock_was_set_seq:	Sequence counter of clock was set events

 * @expires_next:	absolute time of the next event which was scheduled

 *			via clock_set_next_event()

 * @next_timer:		Pointer to the first expiring timer

 * @in_hrtirq:		hrtimer_interrupt() is currently executing

 * @hres_active:	State of high resolution mode

 * @hang_detected:	The last hrtimer interrupt detected a hang
@@ -180,6 +181,10 @@ enum hrtimer_base_type { 
 * @nr_hangs:		Total number of hrtimer interrupt hangs

 * @max_hang_time:	Maximum time spent in hrtimer_interrupt

 * @clock_base:		array of clock bases for this cpu

 *

 * Note: next_timer is just an optimization for __remove_hrtimer().

 *	 Do not dereference the pointer because it is not reliable on

 *	 cross cpu removals.

 */

struct hrtimer_cpu_base {

	raw_spinlock_t			lock;
@@ -191,6 +196,7 @@ struct hrtimer_cpu_base { 
					hres_active	: 1,

					hang_detected	: 1;

	ktime_t				expires_next;

	struct hrtimer			*next_timer;

	unsigned int			nr_events;

	unsigned int			nr_retries;

	unsigned int			nr_hangs;

kernel/time/hrtimer.c

+28 −18
Original line number Diff line number Diff line
@@ -415,12 +415,21 @@ static inline void debug_deactivate(struct hrtimer *timer) 
}



#if defined(CONFIG_NO_HZ_COMMON) || defined(CONFIG_HIGH_RES_TIMERS)

static inline void hrtimer_update_next_timer(struct hrtimer_cpu_base *cpu_base,

					     struct hrtimer *timer)

{

#ifdef CONFIG_HIGH_RES_TIMERS

	cpu_base->next_timer = timer;

#endif

}



static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base)

{

	struct hrtimer_clock_base *base = cpu_base->clock_base;

	ktime_t expires, expires_next = { .tv64 = KTIME_MAX };

	unsigned int active = cpu_base->active_bases;



	hrtimer_update_next_timer(cpu_base, NULL);

	for (; active; base++, active >>= 1) {

		struct timerqueue_node *next;

		struct hrtimer *timer;
@@ -431,8 +440,10 @@ static ktime_t __hrtimer_get_next_event(struct hrtimer_cpu_base *cpu_base) 
		next = timerqueue_getnext(&base->active);

		timer = container_of(next, struct hrtimer, node);

		expires = ktime_sub(hrtimer_get_expires(timer), base->offset);

		if (expires.tv64 < expires_next.tv64)

		if (expires.tv64 < expires_next.tv64) {

			expires_next = expires;

			hrtimer_update_next_timer(cpu_base, timer);

		}

	}

	/*

	 * clock_was_set() might have changed base->offset of any of
@@ -597,6 +608,8 @@ static int hrtimer_reprogram(struct hrtimer *timer, 
	if (cpu_base->in_hrtirq)

		return 0;



	cpu_base->next_timer = timer;



	/*

	 * If a hang was detected in the last timer interrupt then we

	 * do not schedule a timer which is earlier than the expiry
@@ -868,31 +881,28 @@ static void __remove_hrtimer(struct hrtimer *timer, 
			     unsigned long newstate, int reprogram)

{

	struct hrtimer_cpu_base *cpu_base = base->cpu_base;

	struct timerqueue_node *next_timer;

	unsigned int state = timer->state;



	if (!(timer->state & HRTIMER_STATE_ENQUEUED))

		goto out;

	timer->state = newstate;

	if (!(state & HRTIMER_STATE_ENQUEUED))

		return;



	next_timer = timerqueue_getnext(&base->active);

	if (!timerqueue_del(&base->active, &timer->node))

		cpu_base->active_bases &= ~(1 << base->index);



	if (&timer->node == next_timer) {

#ifdef CONFIG_HIGH_RES_TIMERS

		/* Reprogram the clock event device. if enabled */

		if (reprogram && cpu_base->hres_active) {

			ktime_t expires;



			expires = ktime_sub(hrtimer_get_expires(timer),

					    base->offset);

			if (cpu_base->expires_next.tv64 == expires.tv64)

	/*

	 * Note: If reprogram is false we do not update

	 * cpu_base->next_timer. This happens when we remove the first

	 * timer on a remote cpu. No harm as we never dereference

	 * cpu_base->next_timer. So the worst thing what can happen is

	 * an superflous call to hrtimer_force_reprogram() on the

	 * remote cpu later on if the same timer gets enqueued again.

	 */

	if (reprogram && timer == cpu_base->next_timer)

		hrtimer_force_reprogram(cpu_base, 1);

		}

#endif

}

out:

	timer->state = newstate;

}



/*

 * remove hrtimer, called with base lock held