Re: [PATCH v2 3/3] ftrace: add tracepoint for itimer

Mathieu Desnoyers
2009-07-06T13:31:21Z

* Xiao Guangrong (xiaoguangrong@cn.fujitsu.com) wrote:
> Those tracepoints are wanted and useful:
> 1: We can detect a itimer's delay
> 2: We can monitor the lifecycle and behaviors of a itimer
>
> Thus they help in analysing and debuging.
>
> Great thanks to Thomas for giving me so many valuable advices.
>
> There have two case:
> case 1, if we use ITIMER_REAL itimer:
> Example ftrace output:
> main-1649 [001] 1674.034138: hrtimer_start: timer=ce97d3a4 func=it_real_fn expires=1679993510723 ns softexpires=1679993510723 ns
> main-1649 [001] 1674.034140: itimer_state: task=main which=0 state:start timer=ce97d3a4 expires=0 it_value=2.0 it_interval=0.500000
> main-1649 [001] 1676.029184: hrtimer_expire: timer=ce97d3a4 func=it_real_fn now=1679993511197
> main-1649 [001] 1676.029185: hrtimer_cancel: timer=ce97d3a4 func=it_real_fn
> main-1649 [001] 1676.029190: itimer_expire: task=main which=0 now=0
> main-1649 [001] 1676.034744: itimer_state: task=main which=0 state:cancel timer=ce97d3a4 expires=0 it_value=0.0 it_interval=0.0
>
> ITIMER_REAL itime use hrtimer to calculate time, so we can cooperate with
> hrtimer's tracepoint to get it's delay.
>
> from this output information, the process set up a ITIMER_REAL
> iteimr(which=0), use a hrtime which address is ce97d3a4, we can get the
> delay is 1679993511197-1679993510723 = 474 ns
>
> case 2, if we use ITIMER_VIRTUAL/ITIMER_PROF itimer:
> Example ftrace output:
> main-1600 [000] 524.081367: itimer_state: task=main which=2 state:start timer=(null) expires=2008 it_value=2.0 it_interval=0.500000
> main-1600 [000] 526.084820: itimer_expire: task=main which=2 now=2008
> main-1600 [000] 526.088912: itimer_state: task=main which=2 state:cancel timer=(null) expires=0 it_value=0.0 it_interval=0.0
>
> from this, we can know the itimer delay is 2008-2008=0 jiffies.
>
> Changelog v1->v2:
> 1: Remove ktime_to_ns() in TP_fast_assign()
> 2: Combine debugobjects and trace as Thomas's suggestion
>
> Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
> ---
> include/trace/events/timer.h | 66 ++++++++++++++++++++++++++++++++++++++++++
> kernel/itimer.c | 3 ++
> kernel/posix-cpu-timers.c | 3 ++
> 3 files changed, 72 insertions(+), 0 deletions(-)
>
> diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
> index 8ffb2e2..66d33e1 100644
> --- a/include/trace/events/timer.h
> +++ b/include/trace/events/timer.h
> @@ -4,6 +4,7 @@
> #include <linux/tracepoint.h>
> #include <linux/timer.h>
> #include <linux/hrtimer.h>
> +#include <linux/time.h>
>
> #undef TRACE_SYSTEM
> #define TRACE_SYSTEM timer
> @@ -282,6 +283,71 @@ TRACE_EVENT(hrtimer_cancel,
> TP_printk("timer=%p func=%pf", __entry->timer, __entry->function)
> );
>
> +TRACE_EVENT(itimer_state,
> +

Hrm, I'd reserve the use of the *_state namespace for something
different if possible.

In LTTng, we have the ability to list a set of data structures at trace
start (we call this state dump). In this case, we could add a list of
all active timers at trace start. This is useful if the trace started
after timer inits.

So having "_state" without much meaning here might eventually be
confusing.

"_action" or "_call" (like IPCs) might be more appropriate ?

Mathieu

> + TP_PROTO(int which, struct itimerval *value, cputime_t expires),
> +
> + TP_ARGS(which, value, expires),
> +
> + TP_STRUCT__entry(
> + __field( int, which )
> + __field( void *, timer )
> + __field( int, state )
> + __field( cputime_t, expires )
> + __field( long, value_sec )
> + __field( long, value_usec )
> + __field( long, interval_sec )
> + __field( long, interval_usec )
> + __string( comm, current->comm )
> + ),
> +
> + TP_fast_assign(
> + __entry->which = which;
> + __entry->timer = which == ITIMER_REAL ?
> + &current->signal->real_timer : NULL;
> + __entry->state = (value->it_value.tv_sec != 0 ||
> + value->it_value.tv_usec != 0) ? 1 : 0;
> + __entry->expires = which == ITIMER_REAL ? 0 : expires;
> + __entry->value_sec = value->it_value.tv_sec;
> + __entry->value_usec = value->it_value.tv_usec;
> + __entry->interval_sec = value->it_interval.tv_sec;
> + __entry->interval_usec = value->it_interval.tv_usec;
> + __assign_str(comm, current->comm);
> + ),
> +
> + TP_printk("task=%s which=%d state:%s timer=%p expires=%lu "
> + "it_value=%lu.%lu it_interval=%lu.%lu",
> + __get_str(comm), __entry->which,
> + __entry->state ? "start" : "cancel", __entry->timer,
> + __entry->expires, __entry->value_sec, __entry->value_usec,
> + __entry->interval_sec, __entry->interval_usec)
> +);
> +
> +TRACE_EVENT(itimer_expire,
> +
> + TP_PROTO(int which, struct task_struct *task, struct pid *pid, cputime_t now),
> +
> + TP_ARGS(which, task, pid, now),
> +
> + TP_STRUCT__entry(
> + __field( int , which )
> + __field( cputime_t, now )
> + __array( char, comm, TASK_COMM_LEN )
> + ),
> +
> + TP_fast_assign(
> + __entry->which = which;
> + __entry->now = now;
> + if (pid)
> + strcpy(__entry->comm, pid_task(pid, PIDTYPE_PID)->comm);
> + else
> + strcpy(__entry->comm, task->comm);
> + ),
> +
> + TP_printk("task=%s which=%d now=%lu", __entry->comm, __entry->which,
> + __entry->now)
> +);
> +
> #endif /* _TRACE_TIMER_H */
>
> /* This part must be outside protection */
> diff --git a/kernel/itimer.c b/kernel/itimer.c
> index 58762f7..ee3a810 100644
> --- a/kernel/itimer.c
> +++ b/kernel/itimer.c
> @@ -12,6 +12,7 @@
> #include <linux/time.h>
> #include <linux/posix-timers.h>
> #include <linux/hrtimer.h>
> +#include <trace/events/timer.h>
>
> #include <asm/uaccess.h>
>
> @@ -123,6 +124,7 @@ enum hrtimer_restart it_real_fn(struct hrtimer *timer)
> struct signal_struct *sig =
> container_of(timer, struct signal_struct, real_timer);
>
> + trace_itimer_expire(ITIMER_REAL, NULL, sig->leader_pid, 0);
> kill_pid_info(SIGALRM, SEND_SIG_PRIV, sig->leader_pid);
>
> return HRTIMER_NORESTART;
> @@ -220,6 +222,7 @@ again:
> default:
> return -EINVAL;
> }
> + trace_itimer_state(which, value, nval);
> return 0;
> }
>
> diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
> index bece7c0..66d0e28 100644
> --- a/kernel/posix-cpu-timers.c
> +++ b/kernel/posix-cpu-timers.c
> @@ -8,6 +8,7 @@
> #include <linux/math64.h>
> #include <asm/uaccess.h>
> #include <linux/kernel_stat.h>
> +#include <trace/events/timer.h>
>
> /*
> * Called after updating RLIMIT_CPU to set timer expiration if necessary.
> @@ -1160,6 +1161,7 @@ static void check_process_timers(struct task_struct *tsk,
> sig->it_prof_expires = cputime_add(
> sig->it_prof_expires, ptime);
> }
> + trace_itimer_expire(ITIMER_PROF, tsk, NULL, ptime);
> __group_send_sig_info(SIGPROF, SEND_SIG_PRIV, tsk);
> }
> if (!cputime_eq(sig->it_prof_expires, cputime_zero) &&
> @@ -1176,6 +1178,7 @@ static void check_process_timers(struct task_struct *tsk,
> sig->it_virt_expires = cputime_add(
> sig->it_virt_expires, utime);
> }
> + trace_itimer_expire(ITIMER_VIRTUAL, tsk, NULL, utime);
> __group_send_sig_info(SIGVTALRM, SEND_SIG_PRIV, tsk);
> }
> if (!cputime_eq(sig->it_virt_expires, cputime_zero) &&
> --
> 1.6.1.2
>
>

--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68