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: Anna-Maria Gleixner <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: fweisbec@gmail.com
Cc: peterz@infradead.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: https://lkml.kernel.org/r/20190321120921.16463-5-anna-maria@linutronix.de
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 8d7918a..a9b1bbc 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1293,7 +1293,9 @@ int del_timer_sync(struct timer_list *timer)
EXPORT_SYMBOL(del_timer_sync);
#endif
-static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list *))
+static void call_timer_fn(struct timer_list *timer,
+ void (*fn)(struct timer_list *),
+ unsigned long baseclk)
{
int count = preempt_count();
@@ -1316,7 +1318,7 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list
*/
lock_map_acquire(&lockdep_map);
- trace_timer_expire_entry(timer);
+ trace_timer_expire_entry(timer, baseclk);
fn(timer);
trace_timer_expire_exit(timer);
@@ -1337,6 +1339,13 @@ static void call_timer_fn(struct timer_list *timer, void (*fn)(struct timer_list
static void expire_timers(struct timer_base *base, struct hlist_head *head)
{
+ /*
+ * This value is required only for tracing. base->clk was
+ * incremented directly before expire_timers was called. But expiry
+ * is related to the old base->clk value.
+ */
+ unsigned long baseclk = base->clk - 1;
+
while (!hlist_empty(head)) {
struct timer_list *timer;
void (*fn)(struct timer_list *);
@@ -1350,11 +1359,11 @@ static void expire_timers(struct timer_base *base, struct hlist_head *head)
if (timer->flags & TIMER_IRQSAFE) {
raw_spin_unlock(&base->lock);
- call_timer_fn(timer, fn);
+ call_timer_fn(timer, fn, baseclk);
raw_spin_lock(&base->lock);
} else {
raw_spin_unlock_irq(&base->lock);
- call_timer_fn(timer, fn);
+ call_timer_fn(timer, fn, baseclk);
raw_spin_lock_irq(&base->lock);
}
}
