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Commit 2ee3dc80 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
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rcu: Make RCU_FAST_NO_HZ use timer rather than hrtimer 



The RCU_FAST_NO_HZ facility uses an hrtimer to wake up a CPU when
it is allowed to go into dyntick-idle mode, which is almost always
cancelled soon after.  This is not what hrtimers are good at, so
this commit switches to the timer wheel.

Reported-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 2fdbb31b

kernel/rcutree_plugin.h

+12 −28
Original line number Diff line number Diff line
@@ -1980,9 +1980,7 @@ static void rcu_prepare_for_idle(int cpu) 


static DEFINE_PER_CPU(int, rcu_dyntick_drain);

static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);

static DEFINE_PER_CPU(struct hrtimer, rcu_idle_gp_timer);

static ktime_t rcu_idle_gp_wait;	/* If some non-lazy callbacks. */

static ktime_t rcu_idle_lazy_gp_wait;	/* If only lazy callbacks. */

static DEFINE_PER_CPU(struct timer_list, rcu_idle_gp_timer);



/*

 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
@@ -2051,10 +2049,9 @@ static bool rcu_cpu_has_nonlazy_callbacks(int cpu) 
 * real work is done upon re-entry to idle, or by the next scheduling-clock

 * interrupt should idle not be re-entered.

 */

static enum hrtimer_restart rcu_idle_gp_timer_func(struct hrtimer *hrtp)

static void rcu_idle_gp_timer_func(unsigned long unused)

{

	trace_rcu_prep_idle("Timer");

	return HRTIMER_NORESTART;

}



/*
@@ -2062,19 +2059,8 @@ static enum hrtimer_restart rcu_idle_gp_timer_func(struct hrtimer *hrtp) 
 */

static void rcu_prepare_for_idle_init(int cpu)

{

	static int firsttime = 1;

	struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);



	hrtimer_init(hrtp, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

	hrtp->function = rcu_idle_gp_timer_func;

	if (firsttime) {

		unsigned int upj = jiffies_to_usecs(RCU_IDLE_GP_DELAY);



		rcu_idle_gp_wait = ns_to_ktime(upj * (u64)1000);

		upj = jiffies_to_usecs(RCU_IDLE_LAZY_GP_DELAY);

		rcu_idle_lazy_gp_wait = ns_to_ktime(upj * (u64)1000);

		firsttime = 0;

	}

	setup_timer(&per_cpu(rcu_idle_gp_timer, cpu),

		    rcu_idle_gp_timer_func, 0);

}



/*
@@ -2084,7 +2070,7 @@ static void rcu_prepare_for_idle_init(int cpu) 
 */

static void rcu_cleanup_after_idle(int cpu)

{

	hrtimer_cancel(&per_cpu(rcu_idle_gp_timer, cpu));

	del_timer(&per_cpu(rcu_idle_gp_timer, cpu));

	trace_rcu_prep_idle("Cleanup after idle");

}
@@ -2141,11 +2127,11 @@ static void rcu_prepare_for_idle(int cpu) 
		per_cpu(rcu_dyntick_drain, cpu) = 0;

		per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;

		if (rcu_cpu_has_nonlazy_callbacks(cpu))

			hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),

				      rcu_idle_gp_wait, HRTIMER_MODE_REL);

			mod_timer(&per_cpu(rcu_idle_gp_timer, cpu),

					   jiffies + RCU_IDLE_GP_DELAY);

		else

			hrtimer_start(&per_cpu(rcu_idle_gp_timer, cpu),

				      rcu_idle_lazy_gp_wait, HRTIMER_MODE_REL);

			mod_timer(&per_cpu(rcu_idle_gp_timer, cpu),

					   jiffies + RCU_IDLE_LAZY_GP_DELAY);

		return; /* Nothing more to do immediately. */

	} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {

		/* We have hit the limit, so time to give up. */
@@ -2193,14 +2179,12 @@ static void rcu_prepare_for_idle(int cpu) 


static void print_cpu_stall_fast_no_hz(char *cp, int cpu)

{

	struct hrtimer *hrtp = &per_cpu(rcu_idle_gp_timer, cpu);

	struct timer_list *tltp = &per_cpu(rcu_idle_gp_timer, cpu);



	sprintf(cp, "drain=%d %c timer=%lld",

	sprintf(cp, "drain=%d %c timer=%lu",

		per_cpu(rcu_dyntick_drain, cpu),

		per_cpu(rcu_dyntick_holdoff, cpu) == jiffies ? 'H' : '.',

		hrtimer_active(hrtp)

			? ktime_to_us(hrtimer_get_remaining(hrtp))

			: -1);

		timer_pending(tltp) ? tltp->expires - jiffies : -1);

}



#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */