Commit 7f5d42d0 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Trace expedited GP delays due to transitioning CPUs 



If a CPU is transitioning to or from offline state, an expedited
grace period may undergo a timed wait.  This timed wait can unduly
delay grace periods, so this commit adds a trace statement to make
it visible.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 9a414201

include/trace/events/rcu.h

+1 −0
Original line number Diff line number Diff line
@@ -181,6 +181,7 @@ TRACE_EVENT(rcu_grace_period_init, 
 *	"start": Started a real expedited grace period.

 *	"reset": Started resetting the tree

 *	"select": Started selecting the CPUs to wait on.

 *	"selectofl": Selected CPU partially offline.

 *	"startwait": Started waiting on selected CPUs.

 *	"end": Ended a real expedited grace period.

 *	"endwake": Woke piggybackers up.

kernel/rcu/tree_exp.h

+2 −1
Original line number Diff line number Diff line
@@ -32,7 +32,7 @@ static void rcu_exp_gp_seq_start(struct rcu_state *rsp) 
 * Return then value that expedited-grace-period counter will have

 * at the end of the current grace period.

 */

static unsigned long rcu_exp_gp_seq_endval(struct rcu_state *rsp)

static __maybe_unused unsigned long rcu_exp_gp_seq_endval(struct rcu_state *rsp)

{

	return rcu_seq_endval(&rsp->expedited_sequence);

}
@@ -428,6 +428,7 @@ retry_ipi: 
			    (rnp->expmask & mask)) {

				/* Online, so delay for a bit and try again. */

				raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

				trace_rcu_exp_grace_period(rsp->name, rcu_exp_gp_seq_endval(rsp), TPS("selectofl"));

				schedule_timeout_uninterruptible(1);

				goto retry_ipi;

			}

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