Commit dd7dafd1 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make kernel-mode nohz_full CPUs invoke the RCU core processing 



If a nohz_full CPU is idle or executing in userspace, it makes good sense
to keep it out of RCU core processing.  After all, the RCU grace-period
kthread can see its quiescent states and all of its callbacks are
offloaded, so there is nothing for RCU core processing to do.

However, if a nohz_full CPU is executing in kernel space, the RCU
grace-period kthread cannot do anything for it, so such a CPU must report
its own quiescent states.  This commit therefore makes nohz_full CPUs
skip RCU core processing only if the scheduler-clock interrupt caught
them in idle or in userspace.

Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent ed93dfc6

kernel/rcu/tree.c

+5 −5
Original line number Diff line number Diff line
@@ -497,7 +497,7 @@ module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next 
module_param(rcu_kick_kthreads, bool, 0644);



static void force_qs_rnp(int (*f)(struct rcu_data *rdp));

static int rcu_pending(void);

static int rcu_pending(int user);



/*

 * Return the number of RCU GPs completed thus far for debug & stats.
@@ -2267,7 +2267,7 @@ void rcu_sched_clock_irq(int user) 
		__this_cpu_write(rcu_data.rcu_urgent_qs, false);

	}

	rcu_flavor_sched_clock_irq(user);

	if (rcu_pending())

	if (rcu_pending(user))

		invoke_rcu_core();



	trace_rcu_utilization(TPS("End scheduler-tick"));
@@ -2816,7 +2816,7 @@ EXPORT_SYMBOL_GPL(cond_synchronize_rcu); 
 * CPU-local state are performed first.  However, we must check for CPU

 * stalls first, else we might not get a chance.

 */

static int rcu_pending(void)

static int rcu_pending(int user)

{

	bool gp_in_progress;

	struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
@@ -2829,8 +2829,8 @@ static int rcu_pending(void) 
	if (rcu_nocb_need_deferred_wakeup(rdp))

		return 1;



	/* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */

	if (rcu_nohz_full_cpu())

	/* Is this a nohz_full CPU in userspace or idle?  (Ignore RCU if so.) */

	if ((user || rcu_is_cpu_rrupt_from_idle()) && rcu_nohz_full_cpu())

		return 0;



	/* Is the RCU core waiting for a quiescent state from this CPU? */

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