Commit-ID: 9a414201ae7ea089699a0cbd36533345ca17233b
Gitweb: https://git.kernel.org/tip/9a414201ae7ea089699a0cbd36533345ca17233b
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 31 Jan 2018 19:23:24 -0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 20 Feb 2018 16:12:27 -0800
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@xxxxxxxxxxxxxxxxxx>
---
include/trace/events/rcu.h | 3 +++
kernel/rcu/rcu.h | 8 +++++++-
kernel/rcu/tree_exp.h | 12 ++++++++++++
3 files changed, 22 insertions(+), 1 deletion(-)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 0b50fda80db0..e56a618f2a59 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -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.
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 5d13f651cf08..507a0802c717 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -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. */
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 46d61b597731..70ad12abde36 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -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;
--
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