2779ac167b
Documentation/timers/timer_stats.txt claims: "The readout of /proc/timer_stats automatically disables sampling. The sampled information is kept until a new sample period is started. This allows multiple readouts." Some simple testing shows that reading from /proc/timer_stats does not disable sampling. Looking back over past source code, it appears that it never did. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Randy Dunlap <rdunlap@infradead.org> Link: http://lkml.kernel.org/r/53636FB6.9060407@gmail.com [ Small tidyup of the changelog. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
73 lines
3 KiB
Text
73 lines
3 KiB
Text
timer_stats - timer usage statistics
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------------------------------------
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timer_stats is a debugging facility to make the timer (ab)usage in a Linux
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system visible to kernel and userspace developers. If enabled in the config
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but not used it has almost zero runtime overhead, and a relatively small
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data structure overhead. Even if collection is enabled runtime all the
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locking is per-CPU and lookup is hashed.
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timer_stats should be used by kernel and userspace developers to verify that
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their code does not make unduly use of timers. This helps to avoid unnecessary
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wakeups, which should be avoided to optimize power consumption.
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It can be enabled by CONFIG_TIMER_STATS in the "Kernel hacking" configuration
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section.
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timer_stats collects information about the timer events which are fired in a
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Linux system over a sample period:
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- the pid of the task(process) which initialized the timer
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- the name of the process which initialized the timer
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- the function where the timer was initialized
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- the callback function which is associated to the timer
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- the number of events (callbacks)
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timer_stats adds an entry to /proc: /proc/timer_stats
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This entry is used to control the statistics functionality and to read out the
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sampled information.
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The timer_stats functionality is inactive on bootup.
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To activate a sample period issue:
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# echo 1 >/proc/timer_stats
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To stop a sample period issue:
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# echo 0 >/proc/timer_stats
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The statistics can be retrieved by:
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# cat /proc/timer_stats
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While sampling is enabled, each readout from /proc/timer_stats will see
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newly updated statistics. Once sampling is disabled, the sampled information
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is kept until a new sample period is started. This allows multiple readouts.
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Sample output of /proc/timer_stats:
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Timerstats sample period: 3.888770 s
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12, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
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15, 1 swapper hcd_submit_urb (rh_timer_func)
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4, 959 kedac schedule_timeout (process_timeout)
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1, 0 swapper page_writeback_init (wb_timer_fn)
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28, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
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22, 2948 IRQ 4 tty_flip_buffer_push (delayed_work_timer_fn)
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3, 3100 bash schedule_timeout (process_timeout)
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1, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
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1, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
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1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
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1, 2292 ip __netdev_watchdog_up (dev_watchdog)
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1, 23 events/1 do_cache_clean (delayed_work_timer_fn)
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90 total events, 30.0 events/sec
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The first column is the number of events, the second column the pid, the third
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column is the name of the process. The forth column shows the function which
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initialized the timer and in parenthesis the callback function which was
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executed on expiry.
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Thomas, Ingo
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Added flag to indicate 'deferrable timer' in /proc/timer_stats. A deferrable
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timer will appear as follows
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10D, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
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