* Andrew Morton <[email protected]> wrote:
> > /proc/timer-list is useful for profiling applications doing
> > excessive wakeups. With the move towards being tickless, this is
> > more important than ever, and giving users the right tools to find
> > these problems themselves is important.
> >
>
> oic. Nobody ever tells me squat. <updates changelog>
>
> Your explanation doesn't explain why we need this info in a sysrq
> triggerable form.
>
> And what about /proc/timer-stat?
/proc/timer_stats does timer profiling. You start it via:
echo 1 > /proc/timer_stats
and then the profile info gathers into /proc/timer_stats. Useful way to
look at it is:
sort -n /proc/timer_stats
for example:
Timer Stats Version: v0.1
1, 0 swapper page_writeback_init (wb_timer_fn)
1, 1898 modprobe neigh_table_init_no_netlink (neigh_periodic_timer)
1, 1 init schedule_timeout (process_timeout)
1, 1 swapper neigh_table_init_no_netlink (neigh_periodic_timer)
1, 2700 hald-addon-stor do_nanosleep (hrtimer_wakeup)
1, 6 softirq-timer/0 __netdev_watchdog_up (dev_watchdog)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
2, 1 swapper queue_delayed_work_on (delayed_work_timer_fn)
2, 480 IRQ 218 e1000_intr_msi (e1000_watchdog)
3, 2652 yum-updatesd schedule_timeout (process_timeout)
4, 2472 pcscd do_nanosleep (hrtimer_wakeup)
4, 7824 sshd sk_reset_timer (tcp_write_timer)
13, 428 insmod usb_hcd_poll_rh_status (rh_timer_func)
13, 428 insmod usb_hcd_poll_rh_status (rh_timer_func)
13, 437 insmod usb_hcd_submit_urb (rh_timer_func)
19, 21 softirq-net-rx/ sk_reset_timer (tcp_delack_timer)
164, 1868 kondemand/0 queue_delayed_work_on (delayed_work_timer_fn)
164, 1869 kondemand/1 queue_delayed_work_on (delayed_work_timer_fn)
282, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
321, 0 swapper hrtimer_stop_sched_tick (hrtimer_sched_tick)
335, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
408, 0 swapper hrtimer_restart_sched_tick (hrtimer_sched_tick)
1755 total events, 585.534 events/sec
this shows us that the kondemand kernel threads are causing 90% of the
timeout events on this system.
/proc/timer_list shows all currently pending timers, and all the state
of the hardware timers. That is a bit different from timer_stat but
still very useful: it gives us a snapshot into the current state of the
(hr)timer subsystem. I needed it to debug a couple of high-res timers
subsystem bugs. The SysRq trigger was useful for things like timer
related boot hangs. (It's also useful to catch excessive waiters during
bootup.)
Ingo
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