Commit c94a8537 authored by Will Deacon's avatar Will Deacon Committed by Thomas Gleixner
Browse files

tick/broadcast: Prefer per-cpu oneshot wakeup timers to broadcast 



Some SoCs have two per-cpu timer implementations where the timer with the
higher rating stops in deep idle (i.e. suffers from CLOCK_EVT_FEAT_C3STOP)
but is otherwise preferable to the timer with the lower rating. In such a
design, selecting the higher rated devices relies on a global broadcast
timer and IPIs to wake up from deep idle states.

To avoid the reliance on a global broadcast timer and also to reduce the
overhead associated with the IPI wakeups, extend
tick_install_broadcast_device() to manage per-cpu wakeup timers separately
from the broadcast device.

For now, these timers remain unused.

Signed-off-by: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20210524221818.15850-4-will@kernel.org
parent e5007c28

kernel/time/tick-broadcast.c

+58 −1
Original line number Diff line number Diff line
@@ -33,6 +33,8 @@ static int tick_broadcast_forced; 
static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(tick_broadcast_lock);



#ifdef CONFIG_TICK_ONESHOT

static DEFINE_PER_CPU(struct clock_event_device *, tick_oneshot_wakeup_device);



static void tick_broadcast_setup_oneshot(struct clock_event_device *bc);

static void tick_broadcast_clear_oneshot(int cpu);

static void tick_resume_broadcast_oneshot(struct clock_event_device *bc);
@@ -88,13 +90,65 @@ static bool tick_check_broadcast_device(struct clock_event_device *curdev, 
	return !curdev || newdev->rating > curdev->rating;

}



#ifdef CONFIG_TICK_ONESHOT

static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu)

{

	return per_cpu(tick_oneshot_wakeup_device, cpu);

}



static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev,

					   int cpu)

{

	struct clock_event_device *curdev = tick_get_oneshot_wakeup_device(cpu);



	if (!newdev)

		goto set_device;



	if ((newdev->features & CLOCK_EVT_FEAT_DUMMY) ||

	    (newdev->features & CLOCK_EVT_FEAT_C3STOP))

		 return false;



	if (!(newdev->features & CLOCK_EVT_FEAT_PERCPU) ||

	    !(newdev->features & CLOCK_EVT_FEAT_ONESHOT))

		return false;



	if (!cpumask_equal(newdev->cpumask, cpumask_of(cpu)))

		return false;



	if (curdev && newdev->rating <= curdev->rating)

		return false;



	if (!try_module_get(newdev->owner))

		return false;



set_device:

	clockevents_exchange_device(curdev, newdev);

	per_cpu(tick_oneshot_wakeup_device, cpu) = newdev;

	return true;

}

#else

static struct clock_event_device *tick_get_oneshot_wakeup_device(int cpu)

{

	return NULL;

}



static bool tick_set_oneshot_wakeup_device(struct clock_event_device *newdev,

					   int cpu)

{

	return false;

}

#endif



/*

 * Conditionally install/replace broadcast device

 */

void tick_install_broadcast_device(struct clock_event_device *dev)

void tick_install_broadcast_device(struct clock_event_device *dev, int cpu)

{

	struct clock_event_device *cur = tick_broadcast_device.evtdev;



	if (tick_set_oneshot_wakeup_device(dev, cpu))

		return;



	if (!tick_check_broadcast_device(cur, dev))

		return;
@@ -996,6 +1050,9 @@ void hotplug_cpu__broadcast_tick_pull(int deadcpu) 
 */

static void tick_broadcast_oneshot_offline(unsigned int cpu)

{

	if (tick_get_oneshot_wakeup_device(cpu))

		tick_set_oneshot_wakeup_device(NULL, cpu);



	/*

	 * Clear the broadcast masks for the dead cpu, but do not stop

	 * the broadcast device!

kernel/time/tick-common.c

+1 −1
Original line number Diff line number Diff line
@@ -373,7 +373,7 @@ void tick_check_new_device(struct clock_event_device *newdev) 
	/*

	 * Can the new device be used as a broadcast device ?

	 */

	tick_install_broadcast_device(newdev);

	tick_install_broadcast_device(newdev, cpu);

}



/**

kernel/time/tick-internal.h

+2 −2
Original line number Diff line number Diff line
@@ -61,7 +61,7 @@ extern ssize_t sysfs_get_uname(const char *buf, char *dst, size_t cnt); 
/* Broadcasting support */

# ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST

extern int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu);

extern void tick_install_broadcast_device(struct clock_event_device *dev);

extern void tick_install_broadcast_device(struct clock_event_device *dev, int cpu);

extern int tick_is_broadcast_device(struct clock_event_device *dev);

extern void tick_suspend_broadcast(void);

extern void tick_resume_broadcast(void);
@@ -72,7 +72,7 @@ extern int tick_broadcast_update_freq(struct clock_event_device *dev, u32 freq); 
extern struct tick_device *tick_get_broadcast_device(void);

extern struct cpumask *tick_get_broadcast_mask(void);

# else /* !CONFIG_GENERIC_CLOCKEVENTS_BROADCAST: */

static inline void tick_install_broadcast_device(struct clock_event_device *dev) { }

static inline void tick_install_broadcast_device(struct clock_event_device *dev, int cpu) { }

static inline int tick_is_broadcast_device(struct clock_event_device *dev) { return 0; }

static inline int tick_device_uses_broadcast(struct clock_event_device *dev, int cpu) { return 0; }

static inline void tick_do_periodic_broadcast(struct clock_event_device *d) { }