Release 4.7 kernel/time/tick-broadcast-hrtimer.c

/*
 * linux/kernel/time/tick-broadcast-hrtimer.c
 * This file emulates a local clock event device
 * via a pseudo clock device.
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/clockchips.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/module.h>

#include "tick-internal.h"


static struct hrtimer bctimer;



static int bc_shutdown(struct clock_event_device *evt)
{
	/*
         * Note, we cannot cancel the timer here as we might
         * run into the following live lock scenario:
         *
         * cpu 0                cpu1
         * lock(broadcast_lock);
         *                      hrtimer_interrupt()
         *                      bc_handler()
         *                         tick_handle_oneshot_broadcast();
         *                          lock(broadcast_lock);
         * hrtimer_cancel()
         *  wait_for_callback()
         */
	hrtimer_try_to_cancel(&bctimer);
	return 0;
}

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/*
 * This is called from the guts of the broadcast code when the cpu
 * which is about to enter idle has the earliest broadcast timer event.
 */


static int bc_set_next(ktime_t expires, struct clock_event_device *bc)
{
	int bc_moved;
	/*
         * We try to cancel the timer first. If the callback is on
         * flight on some other cpu then we let it handle it. If we
         * were able to cancel the timer nothing can rearm it as we
         * own broadcast_lock.
         *
         * However we can also be called from the event handler of
         * ce_broadcast_hrtimer itself when it expires. We cannot
         * restart the timer because we are in the callback, but we
         * can set the expiry time and let the callback return
         * HRTIMER_RESTART.
         *
         * Since we are in the idle loop at this point and because
         * hrtimer_{start/cancel} functions call into tracing,
         * calls to these functions must be bound within RCU_NONIDLE.
         */
	RCU_NONIDLE({
                        bc_moved = hrtimer_try_to_cancel(&bctimer) >= 0;
                        if (bc_moved)
                                hrtimer_start(&bctimer, expires,
                                              HRTIMER_MODE_ABS_PINNED);});
	if (bc_moved) {
		/* Bind the "device" to the cpu */
		bc->bound_on = smp_processor_id();
	} else if (bc->bound_on == smp_processor_id()) {
		hrtimer_set_expires(&bctimer, expires);
	}
	return 0;
}

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static struct clock_event_device ce_broadcast_hrtimer = {
	.set_state_shutdown	= bc_shutdown,
	.set_next_ktime		= bc_set_next,
	.features		= CLOCK_EVT_FEAT_ONESHOT |
				  CLOCK_EVT_FEAT_KTIME |
				  CLOCK_EVT_FEAT_HRTIMER,
	.rating			= 0,
	.bound_on		= -1,
	.min_delta_ns		= 1,
	.max_delta_ns		= KTIME_MAX,
	.min_delta_ticks	= 1,
	.max_delta_ticks	= ULONG_MAX,
	.mult			= 1,
	.shift			= 0,
	.cpumask		= cpu_all_mask,
};



static enum hrtimer_restart bc_handler(struct hrtimer *t)
{
	ce_broadcast_hrtimer.event_handler(&ce_broadcast_hrtimer);

	if (clockevent_state_oneshot(&ce_broadcast_hrtimer))
		if (ce_broadcast_hrtimer.next_event.tv64 != KTIME_MAX)
			return HRTIMER_RESTART;

	return HRTIMER_NORESTART;
}

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void tick_setup_hrtimer_broadcast(void)
{
	hrtimer_init(&bctimer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
	bctimer.function = bc_handler;
	clockevents_register_device(&ce_broadcast_hrtimer);
}
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Directory: kernel/time

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