About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / timers / timer_stats.txt




Custom Search

Based on kernel version 3.16. Page generated on 2014-08-06 21:41 EST.

1	timer_stats - timer usage statistics
2	------------------------------------
3	
4	timer_stats is a debugging facility to make the timer (ab)usage in a Linux
5	system visible to kernel and userspace developers. If enabled in the config
6	but not used it has almost zero runtime overhead, and a relatively small
7	data structure overhead. Even if collection is enabled runtime all the
8	locking is per-CPU and lookup is hashed.
9	
10	timer_stats should be used by kernel and userspace developers to verify that
11	their code does not make unduly use of timers. This helps to avoid unnecessary
12	wakeups, which should be avoided to optimize power consumption.
13	
14	It can be enabled by CONFIG_TIMER_STATS in the "Kernel hacking" configuration
15	section.
16	
17	timer_stats collects information about the timer events which are fired in a
18	Linux system over a sample period:
19	
20	- the pid of the task(process) which initialized the timer
21	- the name of the process which initialized the timer
22	- the function where the timer was initialized
23	- the callback function which is associated to the timer
24	- the number of events (callbacks)
25	
26	timer_stats adds an entry to /proc: /proc/timer_stats
27	
28	This entry is used to control the statistics functionality and to read out the
29	sampled information.
30	
31	The timer_stats functionality is inactive on bootup.
32	
33	To activate a sample period issue:
34	# echo 1 >/proc/timer_stats
35	
36	To stop a sample period issue:
37	# echo 0 >/proc/timer_stats
38	
39	The statistics can be retrieved by:
40	# cat /proc/timer_stats
41	
42	While sampling is enabled, each readout from /proc/timer_stats will see
43	newly updated statistics. Once sampling is disabled, the sampled information
44	is kept until a new sample period is started. This allows multiple readouts.
45	
46	Sample output of /proc/timer_stats:
47	
48	Timerstats sample period: 3.888770 s
49	  12,     0 swapper          hrtimer_stop_sched_tick (hrtimer_sched_tick)
50	  15,     1 swapper          hcd_submit_urb (rh_timer_func)
51	   4,   959 kedac            schedule_timeout (process_timeout)
52	   1,     0 swapper          page_writeback_init (wb_timer_fn)
53	  28,     0 swapper          hrtimer_stop_sched_tick (hrtimer_sched_tick)
54	  22,  2948 IRQ 4            tty_flip_buffer_push (delayed_work_timer_fn)
55	   3,  3100 bash             schedule_timeout (process_timeout)
56	   1,     1 swapper          queue_delayed_work_on (delayed_work_timer_fn)
57	   1,     1 swapper          queue_delayed_work_on (delayed_work_timer_fn)
58	   1,     1 swapper          neigh_table_init_no_netlink (neigh_periodic_timer)
59	   1,  2292 ip               __netdev_watchdog_up (dev_watchdog)
60	   1,    23 events/1         do_cache_clean (delayed_work_timer_fn)
61	90 total events, 30.0 events/sec
62	
63	The first column is the number of events, the second column the pid, the third
64	column is the name of the process. The forth column shows the function which
65	initialized the timer and in parenthesis the callback function which was
66	executed on expiry.
67	
68	    Thomas, Ingo
69	
70	Added flag to indicate 'deferrable timer' in /proc/timer_stats. A deferrable
71	timer will appear as follows
72	  10D,     1 swapper          queue_delayed_work_on (delayed_work_timer_fn)
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.