Commit d5a9a8c3 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Set a maximum limit for back-to-back callback invocation 



Currently, if a CPU has more than 10,000 callbacks pending, it will
increase rdp->blimit to LONG_MAX.  If you are lucky, LONG_MAX is only
about two billion, but this is still a bit too many callbacks to invoke
back-to-back while otherwise ignoring the world.

This commit therefore sets a maximum limit of DEFAULT_MAX_RCU_BLIMIT,
which is set to 10,000, for rdp->blimit.

Reported-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.ibm.com>
parent 12edff04

kernel/rcu/tree.c

+4 −3
Original line number Diff line number Diff line
@@ -380,7 +380,8 @@ static int rcu_is_cpu_rrupt_from_idle(void) 
	       __this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 1;

}



#define DEFAULT_RCU_BLIMIT 10     /* Maximum callbacks per rcu_do_batch. */

#define DEFAULT_RCU_BLIMIT 10     /* Maximum callbacks per rcu_do_batch ... */

#define DEFAULT_MAX_RCU_BLIMIT 10000 /* ... even during callback flood. */

static long blimit = DEFAULT_RCU_BLIMIT;

#define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */

static long qhimark = DEFAULT_RCU_QHIMARK;
@@ -2113,7 +2114,7 @@ static void rcu_do_batch(struct rcu_data *rdp) 


	/* Reinstate batch limit if we have worked down the excess. */

	count = rcu_segcblist_n_cbs(&rdp->cblist);

	if (rdp->blimit == LONG_MAX && count <= qlowmark)

	if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark)

		rdp->blimit = blimit;



	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
@@ -2354,7 +2355,7 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head, 
			rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);

		} else {

			/* Give the grace period a kick. */

			rdp->blimit = LONG_MAX;

			rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;

			if (rcu_state.n_force_qs == rdp->n_force_qs_snap &&

			    rcu_segcblist_first_pend_cb(&rdp->cblist) != head)

				rcu_force_quiescent_state();

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