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Commit 5e44ce35 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

rcu: Export RCU_FAST_NO_HZ parameters to sysfs 



RCU_FAST_NO_HZ operation is controlled by four compile-time C-preprocessor
macros, but some use cases benefit greatly from runtime adjustment,
particularly when tuning devices.  This commit therefore creates the
corresponding sysfs entries.

Reported-by: default avatarRobin Randhawa <robin.randhawa@arm.com>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent a4889858

kernel/rcutree_plugin.h

+20 −11
Original line number Diff line number Diff line
@@ -1617,6 +1617,15 @@ static void rcu_idle_count_callbacks_posted(void) 
#define RCU_IDLE_GP_DELAY 4		/* Roughly one grace period. */

#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ)	/* Roughly six seconds. */



static int rcu_idle_flushes = RCU_IDLE_FLUSHES;

module_param(rcu_idle_flushes, int, 0644);

static int rcu_idle_opt_flushes = RCU_IDLE_OPT_FLUSHES;

module_param(rcu_idle_opt_flushes, int, 0644);

static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY;

module_param(rcu_idle_gp_delay, int, 0644);

static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;

module_param(rcu_idle_lazy_gp_delay, int, 0644);



extern int tick_nohz_enabled;



/*
@@ -1696,10 +1705,10 @@ int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) 
	}

	/* Set up for the possibility that RCU will post a timer. */

	if (rcu_cpu_has_nonlazy_callbacks(cpu)) {

		*delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,

					  RCU_IDLE_GP_DELAY) - jiffies;

		*delta_jiffies = round_up(rcu_idle_gp_delay + jiffies,

					  rcu_idle_gp_delay) - jiffies;

	} else {

		*delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;

		*delta_jiffies = jiffies + rcu_idle_lazy_gp_delay;

		*delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;

	}

	return 0;
@@ -1805,11 +1814,11 @@ static void rcu_prepare_for_idle(int cpu) 
		if (rcu_cpu_has_nonlazy_callbacks(cpu)) {

			trace_rcu_prep_idle("User dyntick with callbacks");

			rdtp->idle_gp_timer_expires =

				round_up(jiffies + RCU_IDLE_GP_DELAY,

					 RCU_IDLE_GP_DELAY);

				round_up(jiffies + rcu_idle_gp_delay,

					 rcu_idle_gp_delay);

		} else if (rcu_cpu_has_callbacks(cpu)) {

			rdtp->idle_gp_timer_expires =

				round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);

				round_jiffies(jiffies + rcu_idle_lazy_gp_delay);

			trace_rcu_prep_idle("User dyntick with lazy callbacks");

		} else {

			return;
@@ -1861,8 +1870,8 @@ static void rcu_prepare_for_idle(int cpu) 
	/* Check and update the ->dyntick_drain sequencing. */

	if (rdtp->dyntick_drain <= 0) {

		/* First time through, initialize the counter. */

		rdtp->dyntick_drain = RCU_IDLE_FLUSHES;

	} else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&

		rdtp->dyntick_drain = rcu_idle_flushes;

	} else if (rdtp->dyntick_drain <= rcu_idle_opt_flushes &&

		   !rcu_pending(cpu) &&

		   !local_softirq_pending()) {

		/* Can we go dyntick-idle despite still having callbacks? */
@@ -1871,11 +1880,11 @@ static void rcu_prepare_for_idle(int cpu) 
		if (rcu_cpu_has_nonlazy_callbacks(cpu)) {

			trace_rcu_prep_idle("Dyntick with callbacks");

			rdtp->idle_gp_timer_expires =

				round_up(jiffies + RCU_IDLE_GP_DELAY,

					 RCU_IDLE_GP_DELAY);

				round_up(jiffies + rcu_idle_gp_delay,

					 rcu_idle_gp_delay);

		} else {

			rdtp->idle_gp_timer_expires =

				round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);

				round_jiffies(jiffies + rcu_idle_lazy_gp_delay);

			trace_rcu_prep_idle("Dyntick with lazy callbacks");

		}

		tp = &rdtp->idle_gp_timer;