linux-kernel - [PATCH tip/core/rcu 08/17] rcu: Add tracing to irq/NMI dyntick-idle transitions

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Date:   Fri,  1 Dec 2017 11:36:39 -0800
From:   "Paul E. McKenney" <paulmck@...ux.vnet.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,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH tip/core/rcu 08/17] rcu: Add tracing to irq/NMI dyntick-idle transitions

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
 include/trace/events/rcu.h | 14 ++++++++------
 kernel/rcu/tree.c          |  6 ++++++
 2 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 59d40c454aa0..4674b21247f7 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -421,16 +421,18 @@ TRACE_EVENT(rcu_fqs,
 
 /*
  * Tracepoint for dyntick-idle entry/exit events.  These take a string
- * as argument: "Start" for entering dyntick-idle mode, "End" for
- * leaving it, "--=" for events moving towards idle, and "++=" for events
- * moving away from idle.  "Error on entry: not idle task" and "Error on
- * exit: not idle task" indicate that a non-idle task is erroneously
+ * as argument: "Start" for entering dyntick-idle mode, "Startirq" for
+ * entering it from irq/NMI, "End" for leaving it, "Endirq" for leaving it
+ * to irq/NMI, "--=" for events moving towards idle, and "++=" for events
+ * moving away from idle.  "Error on entry: not idle task" and "Error
+ * on exit: not idle task" indicate that a non-idle task is erroneously
  * toying with the idle loop.
  *
  * These events also take a pair of numbers, which indicate the nesting
  * depth before and after the event of interest.  Note that task-related
- * events use the upper bits of each number, while interrupt-related
- * events use the lower bits.
+ * and interrupt-related events use two separate counters, and that the
+ * "++=" and "--=" events for irq/NMI will change the counter by two,
+ * otherwise by one.
  */
 TRACE_EVENT(rcu_dyntick,
 
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 444aa2b3f24d..d069ba2d8412 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -880,12 +880,15 @@ void rcu_nmi_exit(void)
 	 * leave it in non-RCU-idle state.
 	 */
 	if (rdtp->dynticks_nmi_nesting != 1) {
+		trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nmi_nesting,
+				  rdtp->dynticks_nmi_nesting - 2);
 		WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* No store tearing. */
 			   rdtp->dynticks_nmi_nesting - 2);
 		return;
 	}
 
 	/* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
+	trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0);
 	WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
 	rcu_dynticks_eqs_enter();
 }
@@ -1057,6 +1060,9 @@ void rcu_nmi_enter(void)
 		rcu_dynticks_eqs_exit();
 		incby = 1;
 	}
+	trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
+			  rdtp->dynticks_nmi_nesting,
+			  rdtp->dynticks_nmi_nesting + incby);
 	WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* Prevent store tearing. */
 		   rdtp->dynticks_nmi_nesting + incby);
 	barrier();
-- 
2.5.2