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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
This commit is contained in:
Anna-Maria Gleixner 2019-03-21 13:09:21 +01:00 committed by Thomas Gleixner
parent 6849cbb0f9
commit f28d3d5346
2 changed files with 20 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
include/trace/events/timer.h
View File

@ -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)
);
/**

17
kernel/time/timer.c
View File

@ -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);
}
}