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Commit 9d2ad243 authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Paul E. McKenney
Browse files

rcu: Make RCU_FAST_NO_HZ respect nohz= boot parameter 



If the nohz= boot parameter disables nohz, then RCU_FAST_NO_HZ needs to
also disable itself.  This commit therefore checks for tick_nohz_enabled
being zero, disabling rcu_prepare_for_idle() if so.  This commit assumes
that tick_nohz_enabled can change at runtime: If this is not the case,
then a simpler approach suffices.

Signed-off-by: default avatarPaul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 4fa3b6cb

kernel/rcutree.h

+1 −0
Original line number Diff line number Diff line
@@ -97,6 +97,7 @@ struct rcu_dynticks { 
				    /* # times non-lazy CBs posted to CPU. */

	unsigned long nonlazy_posted_snap;

				    /* idle-period nonlazy_posted snapshot. */

	int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */

#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */

};

kernel/rcutree_plugin.h

+15 −0
Original line number Diff line number Diff line
@@ -1971,6 +1971,8 @@ 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. */



extern int tick_nohz_enabled;



/*

 * Does the specified flavor of RCU have non-lazy callbacks pending on

 * the specified CPU?  Both RCU flavor and CPU are specified by the
@@ -2112,6 +2114,7 @@ static void rcu_cleanup_after_idle(int cpu) 


	del_timer(&rdtp->idle_gp_timer);

	trace_rcu_prep_idle("Cleanup after idle");

	rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);

}



/*
@@ -2137,6 +2140,18 @@ static void rcu_prepare_for_idle(int cpu) 
{

	struct timer_list *tp;

	struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);

	int tne;



	/* Handle nohz enablement switches conservatively. */

	tne = ACCESS_ONCE(tick_nohz_enabled);

	if (tne != rdtp->tick_nohz_enabled_snap) {

		if (rcu_cpu_has_callbacks(cpu))

			invoke_rcu_core(); /* force nohz to see update. */

		rdtp->tick_nohz_enabled_snap = tne;

		return;

	}

	if (!tne)

		return;



	/*

	 * If this is an idle re-entry, for example, due to use of

kernel/time/tick-sched.c

+1 −1
Original line number Diff line number Diff line
@@ -105,7 +105,7 @@ static ktime_t tick_init_jiffy_update(void) 
/*

 * NO HZ enabled ?

 */

static int tick_nohz_enabled __read_mostly  = 1;

int tick_nohz_enabled __read_mostly  = 1;



/*

 * Enable / Disable tickless mode