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Commit 5057f55e authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Bind RCU grace-period kthreads if NO_HZ_FULL 



Currently, RCU binds the grace-period kthreads to the timekeeping
CPU only if CONFIG_NO_HZ_FULL_SYSIDLE=y.  This means that these
kthreads must be bound manually when CONFIG_NO_HZ_FULL_SYSIDLE=n and
CONFIG_NO_HZ_FULL=y: Otherwise, these kthreads will induce OS jitter on
random CPUs.  Given that we are trying to reduce the amount of manual
tweaking required to make CONFIG_NO_HZ_FULL=y work nicely, this commit
makes this binding happen when CONFIG_NO_HZ_FULL=y, even in cases where
CONFIG_NO_HZ_FULL_SYSIDLE=n.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
parent 71a9b269

kernel/rcu/tree_plugin.h

+16 −18
Original line number Diff line number Diff line
@@ -2595,20 +2595,6 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp) 
	return rsp == rcu_sysidle_state;

}



/*

 * Bind the grace-period kthread for the sysidle flavor of RCU to the

 * timekeeping CPU.

 */

static void rcu_bind_gp_kthread(void)

{

	int cpu = ACCESS_ONCE(tick_do_timer_cpu);



	if (cpu < 0 || cpu >= nr_cpu_ids)

		return;

	if (raw_smp_processor_id() != cpu)

		set_cpus_allowed_ptr(current, cpumask_of(cpu));

}



/*

 * Return a delay in jiffies based on the number of CPUs, rcu_node

 * leaf fanout, and jiffies tick rate.  The idea is to allow larger
@@ -2819,10 +2805,6 @@ static bool is_sysidle_rcu_state(struct rcu_state *rsp) 
	return false;

}



static void rcu_bind_gp_kthread(void)

{

}



static void rcu_sysidle_report_gp(struct rcu_state *rsp, int isidle,

				  unsigned long maxj)

{
@@ -2853,3 +2835,19 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp) 
#endif /* #ifdef CONFIG_NO_HZ_FULL */

	return 0;

}



/*

 * Bind the grace-period kthread for the sysidle flavor of RCU to the

 * timekeeping CPU.

 */

static void rcu_bind_gp_kthread(void)

{

#ifdef CONFIG_NO_HZ_FULL

	int cpu = ACCESS_ONCE(tick_do_timer_cpu);



	if (cpu < 0 || cpu >= nr_cpu_ids)

		return;

	if (raw_smp_processor_id() != cpu)

		set_cpus_allowed_ptr(current, cpumask_of(cpu));

#endif /* #ifdef CONFIG_NO_HZ_FULL */

}