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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: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2018-01-31 19:23:24 -08:00
parent 274afd6bfa
commit 9a414201ae
3 changed files with 22 additions and 1 deletions
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3
include/trace/events/rcu.h
View File

@ -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.

8
kernel/rcu/rcu.h
View File

@ -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. */

12
kernel/rcu/tree_exp.h
View File

@ -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;