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.

SEE ALSO

       proc(5)