lkml.org 
[lkml]   [2019]   [Mar]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:timers/core] timer/trace: Improve timer tracing
Commit-ID:  f28d3d5346e97e60c81f933ac89ccf015430e5cf
Gitweb: https://git.kernel.org/tip/f28d3d5346e97e60c81f933ac89ccf015430e5cf
Author: Anna-Maria Gleixner <anna-maria@linutronix.de>
AuthorDate: Thu, 21 Mar 2019 13:09:21 +0100
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sun, 24 Mar 2019 20:29:33 +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: 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

---
include/trace/events/timer.h | 11 +++++++----
kernel/time/timer.c | 17 +++++++++++++----
2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index da975d69c453..b7a904825e7d 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -89,24 +89,27 @@ TRACE_EVENT(timer_start,
*/
TRACE_EVENT(timer_expire_entry,

- TP_PROTO(struct timer_list *timer),
+ TP_PROTO(struct timer_list *timer, unsigned long baseclk),

- TP_ARGS(timer),
+ TP_ARGS(timer, baseclk),

TP_STRUCT__entry(
__field( void *, timer )
__field( unsigned long, now )
__field( void *, function)
+ __field( unsigned long, baseclk )
),

TP_fast_assign(
__entry->timer = timer;
__entry->now = jiffies;
__entry->function = timer->function;
+ __entry->baseclk = baseclk;
),

- TP_printk("timer=%p function=%ps now=%lu",
- __entry->timer, __entry->function, __entry->now)
+ TP_printk("timer=%p function=%ps now=%lu baseclk=%lu",
+ __entry->timer, __entry->function, __entry->now,
+ __entry->baseclk)
);

/**
diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index 8d7918ae4d0c..a9b1bbc2d88d 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);
}
}
\
 
 \ /
  Last update: 2019-03-24 21:22    [W:0.087 / U:4.552 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site