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Diffstat (limited to 'kernel/Documentation/timers/timer_stats.txt')
| -rw-r--r-- | kernel/Documentation/timers/timer_stats.txt | 73 |
1 files changed, 73 insertions, 0 deletions
diff --git a/kernel/Documentation/timers/timer_stats.txt b/kernel/Documentation/timers/timer_stats.txt new file mode 100644 index 000000000..de835ee97 --- /dev/null +++ b/kernel/Documentation/timers/timer_stats.txt @@ -0,0 +1,73 @@ +timer_stats - timer usage statistics +------------------------------------ + +timer_stats is a debugging facility to make the timer (ab)usage in a Linux +system visible to kernel and userspace developers. If enabled in the config +but not used it has almost zero runtime overhead, and a relatively small +data structure overhead. Even if collection is enabled runtime all the +locking is per-CPU and lookup is hashed. + +timer_stats should be used by kernel and userspace developers to verify that +their code does not make unduly use of timers. This helps to avoid unnecessary +wakeups, which should be avoided to optimize power consumption. + +It can be enabled by CONFIG_TIMER_STATS in the "Kernel hacking" configuration +section. + +timer_stats collects information about the timer events which are fired in a +Linux system over a sample period: + +- the pid of the task(process) which initialized the timer +- the name of the process which initialized the timer +- the function where the timer was initialized +- the callback function which is associated to the timer +- the number of events (callbacks) + +timer_stats adds an entry to /proc: /proc/timer_stats + +This entry is used to control the statistics functionality and to read out the +sampled information. + +The timer_stats functionality is inactive on bootup. + +To activate a sample period issue: +# echo 1 >/proc/timer_stats + +To stop a sample period issue: +# echo 0 >/proc/timer_stats + +The statistics can be retrieved by: +# cat /proc/timer_stats + +While sampling is enabled, each readout from /proc/timer_stats will see +newly updated statistics. Once sampling is disabled, the sampled information +is kept until a new sample period is started. This allows multiple readouts. + +Sample output of /proc/timer_stats: + +Timerstats sample period: 3.888770 s + 12, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick) + 15, 1 swapper hcd_submit_urb (rh_timer_func) + 4, 959 kedac schedule_timeout (process_timeout) + 1, 0 swapper page_writeback_init (wb_timer_fn) + 28, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick) + 22, 2948 IRQ 4 tty_flip_buffer_push (delayed_work_timer_fn) + 3, 3100 bash schedule_timeout (process_timeout) + 1, 1 swapper queue_delayed_work_on (delayed_work_timer_fn) + 1, 1 swapper queue_delayed_work_on (delayed_work_timer_fn) + 1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer) + 1, 2292 ip __netdev_watchdog_up (dev_watchdog) + 1, 23 events/1 do_cache_clean (delayed_work_timer_fn) +90 total events, 30.0 events/sec + +The first column is the number of events, the second column the pid, the third +column is the name of the process. The forth column shows the function which +initialized the timer and in parenthesis the callback function which was +executed on expiry. + + Thomas, Ingo + +Added flag to indicate 'deferrable timer' in /proc/timer_stats. A deferrable +timer will appear as follows + 10D, 1 swapper queue_delayed_work_on (delayed_work_timer_fn) + |