[lttng-dev] [PATCH lttng-modules 1/5] fix: timer/trace: Improve timer tracing (v5.2)

[mjeanson@efficios.com (Michael Jeanson)]

See upstream commit:

  commit f28d3d5346e97e60c81f933ac89ccf015430e5cf
  Author: Anna-Maria Gleixner <anna-maria at linutronix.de>
  Date:   Thu Mar 21 13:09:21 2019 +0100

    timer/trace: Improve timer tracing

    Timers are added to the timer wheel off by one. This is required in
    case a timer is queued directly before incrementing jiffies to prevent
    early timer expiry.

    When reading a timer trace and relying only on the expiry time of the timer
    in the timer_start trace point and on the now in the timer_expiry_entry
    trace point, it seems that the timer fires late. With the current
    timer_expiry_entry trace point information only now=jiffies is printed but
    not the value of base->clk. This makes it impossible to draw a conclusion
    to the index of base->clk and makes it impossible to examine timer problems
    without additional trace points.

    Therefore add the base->clk value to the timer_expire_entry trace
    point, to be able to calculate the index the timer base is located at
    during collecting expired timers.

Signed-off-by: Michael Jeanson <mjeanson at efficios.com>
---
 instrumentation/events/lttng-module/timer.h | 22 +++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/instrumentation/events/lttng-module/timer.h b/instrumentation/events/lttng-module/timer.h
index 8703ea0..997084f 100644
--- a/instrumentation/events/lttng-module/timer.h
+++ b/instrumentation/events/lttng-module/timer.h
@@ -89,6 +89,27 @@ LTTNG_TRACEPOINT_EVENT(timer_start,
 )
 #endif /* #else #if (LINUX_VERSION_CODE >= KERNEL_VERSION(4,2,0)) */
 
+#if (LINUX_VERSION_CODE >= KERNEL_VERSION(5,2,0))
+/**
+ * timer_expire_entry - called immediately before the timer callback
+ * @timer:	pointer to struct timer_list
+ *
+ * Allows to determine the timer latency.
+ */
+LTTNG_TRACEPOINT_EVENT(timer_expire_entry,
+
+	TP_PROTO(struct timer_list *timer, unsigned long baseclk),
+
+	TP_ARGS(timer, baseclk),
+
+	TP_FIELDS(
+		ctf_integer_hex(void *, timer, timer)
+		ctf_integer(unsigned long, now, jiffies)
+		ctf_integer_hex(void *, function, timer->function)
+		ctf_integer(unsigned long, baseclk, baseclk)
+	)
+)
+#else
 /**
  * timer_expire_entry - called immediately before the timer callback
  * @timer:	pointer to struct timer_list
@@ -107,6 +128,7 @@ LTTNG_TRACEPOINT_EVENT(timer_expire_entry,
 		ctf_integer_hex(void *, function, timer->function)
 	)
 )
+#endif
 
 /**
  * timer_expire_exit - called immediately after the timer callback returns
-- 
2.17.1