Commit-ID: 7f5d42d05155523a4c42c2c5170f2a368217aed5
Gitweb: https://git.kernel.org/tip/7f5d42d05155523a4c42c2c5170f2a368217aed5
Author: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
AuthorDate: Wed, 31 Jan 2018 19:40:22 -0800
Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
CommitDate: Tue, 20 Feb 2018 16:12:28 -0800
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: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
include/trace/events/rcu.h | 1 +
kernel/rcu/tree_exp.h | 3 ++-
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index e56a618f2a59..d8c33298c153 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -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.
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 70ad12abde36..fecb6b6ab452 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -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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