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Commit 9a414201 authored by Paul E. McKenney's avatar Paul E. McKenney
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rcu: Add more tracing of expedited grace periods 



This commit adds more tracing of expedited grace periods to enable
improved debugging of slowdowns.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 274afd6b

include/trace/events/rcu.h

+3 −0
Original line number Diff line number Diff line
@@ -179,6 +179,9 @@ TRACE_EVENT(rcu_grace_period_init, 
 *

 *	"snap": Captured snapshot of expedited grace period sequence number.

 *	"start": Started a real expedited grace period.

 *	"reset": Started resetting the tree

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

 *	"startwait": Started waiting on selected CPUs.

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

 *	"endwake": Woke piggybackers up.

 *	"done": Someone else did the expedited grace period for us.

kernel/rcu/rcu.h

+7 −1
Original line number Diff line number Diff line
@@ -77,12 +77,18 @@ static inline void rcu_seq_start(unsigned long *sp) 
	WARN_ON_ONCE(rcu_seq_state(*sp) != 1);

}



/* Compute the end-of-grace-period value for the specified sequence number. */

static inline unsigned long rcu_seq_endval(unsigned long *sp)

{

	return (*sp | RCU_SEQ_STATE_MASK) + 1;

}



/* Adjust sequence number for end of update-side operation. */

static inline void rcu_seq_end(unsigned long *sp)

{

	smp_mb(); /* Ensure update-side operation before counter increment. */

	WARN_ON_ONCE(!rcu_seq_state(*sp));

	WRITE_ONCE(*sp, (*sp | RCU_SEQ_STATE_MASK) + 1);

	WRITE_ONCE(*sp, rcu_seq_endval(sp));

}



/* Take a snapshot of the update side's sequence number. */

kernel/rcu/tree_exp.h

+12 −0
Original line number Diff line number Diff line
@@ -28,6 +28,15 @@ static void rcu_exp_gp_seq_start(struct rcu_state *rsp) 
	rcu_seq_start(&rsp->expedited_sequence);

}



/*

 * 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)

{

	return rcu_seq_endval(&rsp->expedited_sequence);

}



/*

 * Record the end of an expedited grace period.

 */
@@ -366,7 +375,9 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, 
	int ret;

	struct rcu_node *rnp;



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

	sync_exp_reset_tree(rsp);

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

	rcu_for_each_leaf_node(rsp, rnp) {

		raw_spin_lock_irqsave_rcu_node(rnp, flags);
@@ -443,6 +454,7 @@ static void synchronize_sched_expedited_wait(struct rcu_state *rsp) 
	struct rcu_node *rnp_root = rcu_get_root(rsp);

	int ret;



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

	jiffies_stall = rcu_jiffies_till_stall_check();

	jiffies_start = jiffies;