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Commit 301bc715 authored by Srivatsa Vaddagiri's avatar Srivatsa Vaddagiri Committed by Pavankumar Kondeti
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hrtimer: reprogram remote CPU's timer hardware 



Currently it is not possible to queue a hrtimer on a remote CPU
that expires before any other existing timer on that CPU. Send
an IPI to remote CPU to reprogram the hardware to get rid of
this limitation.

Change-Id: I69f6a267bb65e558ec35f802d678a67ba1ee1c29
Signed-off-by: default avatarSrivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: default avatarPavankumar Kondeti <pkondeti@codeaurora.org>
parent 022b6fdc

kernel/time/hrtimer.c

+38 −40
Original line number Diff line number Diff line
@@ -49,6 +49,7 @@ 
#include <linux/sched/deadline.h>

#include <linux/timer.h>

#include <linux/freezer.h>

#include <linux/irq_work.h>



#include <asm/uaccess.h>
@@ -167,29 +168,6 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer, 
	}

}



/*

 * With HIGHRES=y we do not migrate the timer when it is expiring

 * before the next event on the target cpu because we cannot reprogram

 * the target cpu hardware and we would cause it to fire late.

 *

 * Called with cpu_base->lock of target cpu held.

 */

static int

hrtimer_check_target(struct hrtimer *timer, struct hrtimer_clock_base *new_base)

{

#ifdef CONFIG_HIGH_RES_TIMERS

	ktime_t expires;



	if (!new_base->cpu_base->hres_active)

		return 0;



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

	return expires.tv64 <= new_base->cpu_base->expires_next.tv64;

#else

	return 0;

#endif

}



/*

 * Switch the timer base to the current CPU when possible.

 */
@@ -199,11 +177,9 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base, 
{

	struct hrtimer_clock_base *new_base;

	struct hrtimer_cpu_base *new_cpu_base;

	int this_cpu = smp_processor_id();

	int cpu = get_nohz_timer_target(pinned);

	int basenum = base->index;



again:

	new_cpu_base = &per_cpu(hrtimer_bases, cpu);

	new_base = &new_cpu_base->clock_base[basenum];
@@ -224,20 +200,7 @@ again: 
		timer->base = NULL;

		raw_spin_unlock(&base->cpu_base->lock);

		raw_spin_lock(&new_base->cpu_base->lock);



		if (cpu != this_cpu && hrtimer_check_target(timer, new_base)) {

			cpu = this_cpu;

			raw_spin_unlock(&new_base->cpu_base->lock);

			raw_spin_lock(&base->cpu_base->lock);

			timer->base = base;

			goto again;

		}

		timer->base = new_base;

	} else {

		if (cpu != this_cpu && hrtimer_check_target(timer, new_base)) {

			cpu = this_cpu;

			goto again;

		}

	}

	return new_base;

}
@@ -657,6 +620,20 @@ static void retrigger_next_event(void *arg) 
	raw_spin_unlock(&base->lock);

}



#ifdef CONFIG_SMP

static void raise_hrtimer_softirq(struct irq_work *arg)

{

	if (!hrtimer_hres_active())

		return;



	raise_softirq(HRTIMER_SOFTIRQ);

}



static DEFINE_PER_CPU(struct irq_work, hrtimer_kick_work) = {

	.func = raise_hrtimer_softirq,

};

#endif



/*

 * Switch to high resolution mode

 */
@@ -721,6 +698,22 @@ static inline void retrigger_next_event(void *arg) { } 


#endif /* CONFIG_HIGH_RES_TIMERS */



#ifdef CONFIG_SMP



static void kick_remote_cpu(int cpu)

{

	get_cpu();

	if (cpu_online(cpu))

		irq_work_queue_on(&per_cpu(hrtimer_kick_work, cpu), cpu);

	put_cpu();

}



#else



static inline void kick_remote_cpu(int cpu) { }



#endif



/*

 * Clock realtime was set

 *
@@ -939,7 +932,7 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, 
{

	struct hrtimer_clock_base *base, *new_base;

	unsigned long flags;

	int ret, leftmost;

	int ret, leftmost, kick = 0, cpu;



	base = lock_hrtimer_base(timer, &flags);
@@ -986,7 +979,6 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, 
		 * Only allow reprogramming if the new base is on this CPU.

		 * (it might still be on another CPU if the timer was pending)

		 *

		 * XXX send_remote_softirq() ?

		 */

		if (wakeup) {

			/*
@@ -1000,10 +992,16 @@ int __hrtimer_start_range_ns(struct hrtimer *timer, ktime_t tim, 
		} else {

			__raise_softirq_irqoff(HRTIMER_SOFTIRQ);

		}

	} else {

		cpu = new_base->cpu_base->cpu;

		kick = (leftmost && (cpu != smp_processor_id()));

	}



	unlock_hrtimer_base(timer, &flags);



	if (kick)

		kick_remote_cpu(cpu);



	return ret;

}

EXPORT_SYMBOL_GPL(__hrtimer_start_range_ns);