linux-kernel - [PATCH tip/core/rcu 06/14] rcu: Add jiffies-since-GP-activity to show_rcu_gp

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Date:   Sun, 11 Nov 2018 11:28:56 -0800
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     linux-kernel@...r.kernel.org
Cc:     mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org,
        rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
        fweisbec@...il.com, oleg@...hat.com, joel@...lfernandes.org,
        "Paul E. McKenney" <paulmck@...ux.ibm.com>
Subject: [PATCH tip/core/rcu 06/14] rcu: Add jiffies-since-GP-activity to show_rcu_gp_kthreads()

This commit adds a printout of the number of jiffies since the last time
that the RCU grace-period kthread did any processing.  This can be useful
when tracking down forward-progress issues.

Signed-off-by: Paul E. McKenney <paulmck@...ux.ibm.com>
---
 kernel/rcu/tree.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ea78532183ac..e7c9848d1e1b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -515,12 +515,14 @@ static const char *gp_state_getname(short gs)
 void show_rcu_gp_kthreads(void)
 {
 	int cpu;
+	unsigned long j;
 	struct rcu_data *rdp;
 	struct rcu_node *rnp;
 
-	pr_info("%s: wait state: %s(%d) ->state: %#lx\n", rcu_state.name,
-		gp_state_getname(rcu_state.gp_state), rcu_state.gp_state,
-		rcu_state.gp_kthread->state);
+	j = jiffies - READ_ONCE(rcu_state.gp_activity);
+	pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %ld\n",
+		rcu_state.name, gp_state_getname(rcu_state.gp_state),
+		rcu_state.gp_state, rcu_state.gp_kthread->state, j);
 	rcu_for_each_node_breadth_first(rnp) {
 		if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed))
 			continue;
-- 
2.17.1