NAME¶
/proc/timer_stats - timer statistics
DESCRIPTION¶
- /proc/timer_stats (from Linux 2.6.21 until Linux 4.10)
- This is a debugging facility to make timer (ab)use in a Linux system
visible to kernel and user-space developers. It can be used by kernel and
user-space developers to verify that their code does not make undue use of
timers. The goal is to avoid unnecessary wakeups, thereby optimizing power
consumption.
- If enabled in the kernel (CONFIG_TIMER_STATS), but not used, it has
almost zero run-time overhead and a relatively small data-structure
overhead. Even if collection is enabled at run time, overhead is low: all
the locking is per-CPU and lookup is hashed.
- The /proc/timer_stats file is used both to control sampling
facility and to read out the sampled information.
- The timer_stats functionality is inactive on bootup. A sampling
period can be started using the following command:
-
# echo 1 > /proc/timer_stats
- The following command stops a sampling period:
-
# 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 from /proc/timer_stats:
-
$ cat /proc/timer_stats
Timer Stats Version: v0.3
Sample period: 1.764 s
Collection: active
255, 0 swapper/3 hrtimer_start_range_ns (tick_sched_timer)
71, 0 swapper/1 hrtimer_start_range_ns (tick_sched_timer)
58, 0 swapper/0 hrtimer_start_range_ns (tick_sched_timer)
4, 1694 gnome-shell mod_delayed_work_on (delayed_work_timer_fn)
17, 7 rcu_sched rcu_gp_kthread (process_timeout)
...
1, 4911 kworker/u16:0 mod_delayed_work_on (delayed_work_timer_fn)
1D, 2522 kworker/0:0 queue_delayed_work_on (delayed_work_timer_fn)
1029 total events, 583.333 events/sec
- The output columns are:
- [1]
- a count of the number of events, optionally (since Linux 2.6.23) followed
by the letter 'D' if this is a deferrable timer;
- [2]
- the PID of the process that initialized the timer;
- [3]
- the name of the process that initialized the timer;
- [4]
- the function where the timer was initialized; and (in parentheses) the
callback function that is associated with the timer.
- During the Linux 4.11 development cycle, this file was removed because of
security concerns, as it exposes information across namespaces.
Furthermore, it is possible to obtain the same information via in-kernel
tracing facilities such as ftrace.