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1timer_stats - timer usage statistics
2------------------------------------
3
4timer_stats is a debugging facility to make the timer (ab)usage in a Linux
5system visible to kernel and userspace developers. It is not intended for
6production usage as it adds significant overhead to the (hr)timer code and the
7(hr)timer data structures.
8
9timer_stats should be used by kernel and userspace developers to verify that
10their code does not make unduly use of timers. This helps to avoid unnecessary
11wakeups, which should be avoided to optimize power consumption.
12
13It can be enabled by CONFIG_TIMER_STATS in the "Kernel hacking" configuration
14section.
15
16timer_stats collects information about the timer events which are fired in a
17Linux system over a sample period:
18
19- the pid of the task(process) which initialized the timer
20- the name of the process which initialized the timer
21- the function where the timer was intialized
22- the callback function which is associated to the timer
23- the number of events (callbacks)
24
25timer_stats adds an entry to /proc: /proc/timer_stats
26
27This entry is used to control the statistics functionality and to read out the
28sampled information.
29
30The timer_stats functionality is inactive on bootup.
31
32To activate a sample period issue:
33# echo 1 >/proc/timer_stats
34
35To stop a sample period issue:
36# echo 0 >/proc/timer_stats
37
38The statistics can be retrieved by:
39# cat /proc/timer_stats
40
41The readout of /proc/timer_stats automatically disables sampling. The sampled
42information is kept until a new sample period is started. This allows multiple
43readouts.
44
45Sample output of /proc/timer_stats:
46
47Timerstats sample period: 3.888770 s
48 12, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
49 15, 1 swapper hcd_submit_urb (rh_timer_func)
50 4, 959 kedac schedule_timeout (process_timeout)
51 1, 0 swapper page_writeback_init (wb_timer_fn)
52 28, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
53 22, 2948 IRQ 4 tty_flip_buffer_push (delayed_work_timer_fn)
54 3, 3100 bash schedule_timeout (process_timeout)
55 1, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
56 1, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
57 1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
58 1, 2292 ip __netdev_watchdog_up (dev_watchdog)
59 1, 23 events/1 do_cache_clean (delayed_work_timer_fn)
6090 total events, 30.0 events/sec
61
62The first column is the number of events, the second column the pid, the third
63column is the name of the process. The forth column shows the function which
64initialized the timer and in parantheses the callback function which was
65executed on expiry.
66
67 Thomas, Ingo
68