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Commit 82f67cd9 authored by Ingo Molnar's avatar Ingo Molnar Committed by Linus Torvalds
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[PATCH] Add debugging feature /proc/timer_stat 



Add /proc/timer_stats support: debugging feature to profile timer expiration.
Both the starting site, process/PID and the expiration function is captured.
This allows the quick identification of timer event sources in a system.

Sample output:

# echo 1 > /proc/timer_stats
# cat /proc/timer_stats
Timer Stats Version: v0.1
Sample period: 4.010 s
  24,     0 swapper          hrtimer_stop_sched_tick (hrtimer_sched_tick)
  11,     0 swapper          sk_reset_timer (tcp_delack_timer)
   6,     0 swapper          hrtimer_stop_sched_tick (hrtimer_sched_tick)
   2,     1 swapper          queue_delayed_work_on (delayed_work_timer_fn)
  17,     0 swapper          hrtimer_restart_sched_tick (hrtimer_sched_tick)
   2,     1 swapper          queue_delayed_work_on (delayed_work_timer_fn)
   4,  2050 pcscd            do_nanosleep (hrtimer_wakeup)
   5,  4179 sshd             sk_reset_timer (tcp_write_timer)
   4,  2248 yum-updatesd     schedule_timeout (process_timeout)
  18,     0 swapper          hrtimer_restart_sched_tick (hrtimer_sched_tick)
   3,     0 swapper          sk_reset_timer (tcp_delack_timer)
   1,     1 swapper          neigh_table_init_no_netlink (neigh_periodic_timer)
   2,     1 swapper          e1000_up (e1000_watchdog)
   1,     1 init             schedule_timeout (process_timeout)
100 total events, 25.24 events/sec

[ cleanups and hrtimers support from Thomas Gleixner <tglx@linutronix.de> ]
[bunk@stusta.de: nr_entries can become static]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAdrian Bunk <bunk@stusta.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8bfd9a7a

Documentation/hrtimer/timer_stats.txt

0 → 100644
+68 −0
Original line number Diff line number Diff line 
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. It is not intended for

production usage as it adds significant overhead to the (hr)timer code and the

(hr)timer data structures.



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 intialized

- 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



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.



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 parantheses the callback function which was

executed on expiry.



    Thomas, Ingo

include/linux/hrtimer.h

+45 −0
Original line number Diff line number Diff line
@@ -119,6 +119,11 @@ struct hrtimer { 
	enum hrtimer_cb_mode		cb_mode;

	struct list_head		cb_entry;

#endif

#ifdef CONFIG_TIMER_STATS

	void				*start_site;

	char				start_comm[16];

	int				start_pid;

#endif

};



/**
@@ -311,4 +316,44 @@ extern unsigned long ktime_divns(const ktime_t kt, s64 div); 
# define ktime_divns(kt, div)		(unsigned long)((kt).tv64 / (div))

#endif



/*

 * Timer-statistics info:

 */

#ifdef CONFIG_TIMER_STATS



extern void timer_stats_update_stats(void *timer, pid_t pid, void *startf,

				     void *timerf, char * comm);



static inline void timer_stats_account_hrtimer(struct hrtimer *timer)

{

	timer_stats_update_stats(timer, timer->start_pid, timer->start_site,

				 timer->function, timer->start_comm);

}



extern void __timer_stats_hrtimer_set_start_info(struct hrtimer *timer,

						 void *addr);



static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)

{

	__timer_stats_hrtimer_set_start_info(timer, __builtin_return_address(0));

}



static inline void timer_stats_hrtimer_clear_start_info(struct hrtimer *timer)

{

	timer->start_site = NULL;

}

#else

static inline void timer_stats_account_hrtimer(struct hrtimer *timer)

{

}



static inline void timer_stats_hrtimer_set_start_info(struct hrtimer *timer)

{

}



static inline void timer_stats_hrtimer_clear_start_info(struct hrtimer *timer)

{

}

#endif



#endif

include/linux/timer.h

+54 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#define _LINUX_TIMER_H



#include <linux/list.h>

#include <linux/ktime.h>

#include <linux/spinlock.h>

#include <linux/stddef.h>
@@ -15,6 +16,11 @@ struct timer_list { 
	unsigned long data;



	struct tvec_t_base_s *base;

#ifdef CONFIG_TIMER_STATS

	void *start_site;

	char start_comm[16];

	int start_pid;

#endif

};



extern struct tvec_t_base_s boot_tvec_bases;
@@ -73,6 +79,54 @@ extern unsigned long next_timer_interrupt(void); 
 */

extern unsigned long get_next_timer_interrupt(unsigned long now);



/*

 * Timer-statistics info:

 */

#ifdef CONFIG_TIMER_STATS



extern void init_timer_stats(void);



extern void timer_stats_update_stats(void *timer, pid_t pid, void *startf,

				     void *timerf, char * comm);



static inline void timer_stats_account_timer(struct timer_list *timer)

{

	timer_stats_update_stats(timer, timer->start_pid, timer->start_site,

				 timer->function, timer->start_comm);

}



extern void __timer_stats_timer_set_start_info(struct timer_list *timer,

					       void *addr);



static inline void timer_stats_timer_set_start_info(struct timer_list *timer)

{

	__timer_stats_timer_set_start_info(timer, __builtin_return_address(0));

}



static inline void timer_stats_timer_clear_start_info(struct timer_list *timer)

{

	timer->start_site = NULL;

}

#else

static inline void init_timer_stats(void)

{

}



static inline void timer_stats_account_timer(struct timer_list *timer)

{

}



static inline void timer_stats_timer_set_start_info(struct timer_list *timer)

{

}



static inline void timer_stats_timer_clear_start_info(struct timer_list *timer)

{

}

#endif



extern void delayed_work_timer_fn(unsigned long __data);



/**

 * add_timer - start a timer

 * @timer: the timer to be added

kernel/hrtimer.c

+26 −0
Original line number Diff line number Diff line
@@ -585,6 +585,18 @@ static inline void hrtimer_init_timer_hres(struct hrtimer *timer) { } 


#endif /* CONFIG_HIGH_RES_TIMERS */



#ifdef CONFIG_TIMER_STATS

void __timer_stats_hrtimer_set_start_info(struct hrtimer *timer, void *addr)

{

	if (timer->start_site)

		return;



	timer->start_site = addr;

	memcpy(timer->start_comm, current->comm, TASK_COMM_LEN);

	timer->start_pid = current->pid;

}

#endif



/*

 * Counterpart to lock_timer_base above:

 */
@@ -743,6 +755,7 @@ remove_hrtimer(struct hrtimer *timer, struct hrtimer_clock_base *base) 
		 * reprogramming happens in the interrupt handler. This is a

		 * rare case and less expensive than a smp call.

		 */

		timer_stats_hrtimer_clear_start_info(timer);

		reprogram = base->cpu_base == &__get_cpu_var(hrtimer_bases);

		__remove_hrtimer(timer, base, HRTIMER_STATE_INACTIVE,

				 reprogram);
@@ -791,6 +804,8 @@ hrtimer_start(struct hrtimer *timer, ktime_t tim, const enum hrtimer_mode mode) 
	}

	timer->expires = tim;



	timer_stats_hrtimer_set_start_info(timer);



	enqueue_hrtimer(timer, new_base, base == new_base);



	unlock_hrtimer_base(timer, &flags);
@@ -925,6 +940,12 @@ void hrtimer_init(struct hrtimer *timer, clockid_t clock_id, 


	timer->base = &cpu_base->clock_base[clock_id];

	hrtimer_init_timer_hres(timer);



#ifdef CONFIG_TIMER_STATS

	timer->start_site = NULL;

	timer->start_pid = -1;

	memset(timer->start_comm, 0, TASK_COMM_LEN);

#endif

}

EXPORT_SYMBOL_GPL(hrtimer_init);
@@ -1006,6 +1027,7 @@ void hrtimer_interrupt(struct clock_event_device *dev) 


			__remove_hrtimer(timer, base,

					 HRTIMER_STATE_CALLBACK, 0);

			timer_stats_account_hrtimer(timer);



			/*

			 * Note: We clear the CALLBACK bit after
@@ -1050,6 +1072,8 @@ static void run_hrtimer_softirq(struct softirq_action *h) 
		timer = list_entry(cpu_base->cb_pending.next,

				   struct hrtimer, cb_entry);



		timer_stats_account_hrtimer(timer);



		fn = timer->function;

		__remove_hrtimer(timer, timer->base, HRTIMER_STATE_CALLBACK, 0);

		spin_unlock_irq(&cpu_base->lock);
@@ -1106,6 +1130,8 @@ static inline void run_hrtimer_queue(struct hrtimer_cpu_base *cpu_base, 
		if (base->softirq_time.tv64 <= timer->expires.tv64)

			break;



		timer_stats_account_hrtimer(timer);



		fn = timer->function;

		__remove_hrtimer(timer, base, HRTIMER_STATE_CALLBACK, 0);

		spin_unlock_irq(&cpu_base->lock);

kernel/time/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -5,3 +5,4 @@ obj-$(CONFIG_GENERIC_CLOCKEVENTS) += tick-common.o 
obj-$(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST)	+= tick-broadcast.o

obj-$(CONFIG_TICK_ONESHOT)			+= tick-oneshot.o

obj-$(CONFIG_TICK_ONESHOT)			+= tick-sched.o

obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o