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Subject[PATCH v3 4/4] ftrace: add tracepoint for itimer
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-1517 [000] 288.826521: hrtimer_start: timer=ce807544 func=it_real_fn expires=289327664443 ns softexpires=289327664443 ns
main-1517 [000] 288.826524: itimer_state: which=0 expires=0 it_value=0.500 it_interval=0.0
main-1517 [000] 288.827313: hrtimer_expire: timer=ce807544 now=289327958161 ns
main-1517 [000] 288.827314: hrtimer_cancel: timer=ce807544
main-1517 [000] 288.827315: itimer_expire: pid=1517 which=0 now=0
main-1517 [000] 288.827319: hrtimer_callback_done: timer=ce807544
main-1517 [000] 288.827463: itimer_state: which=0 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 ce807544, we can get the
delay is 289327958161-289327664443=293718 ns

case 2, if we use ITIMER_VIRTUAL/ITIMER_PROF itimer:
Example ftrace output:
main-5409 [001] 12763.874835: itimer_state: which=1 expires=2 it_value=0.500 it_interval=0.500
main-5409 [001] 12763.883495: itimer_expire: pid=5409 which=1 now=2
main-5409 [001] 12763.883712: itimer_state: which=1 expires=0 it_value=0.0 it_interval=0.0

from this, we can know the itimer delay is 2-2=0 jiffies.

Changelog:
v1->v2:
Remove ktime_to_ns() in TP_fast_assign()
v2->v3:
Below changes are all base on Thomas's suggestion:
1: Remove ITIMER_REAL's timer address and 'state' from trace_itimer_state()
2: Don't save task's name in trace_itimer_state()
3: Save task's pid instead of task's name in trace_itimer_expire()

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
---
include/trace/events/timer.h | 52 ++++++++++++++++++++++++++++++++++++++++++
kernel/itimer.c | 5 +++-
kernel/posix-cpu-timers.c | 3 ++
3 files changed, 59 insertions(+), 1 deletions(-)

diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index 8b22b12..0a77f34 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -237,6 +237,58 @@ TRACE_EVENT(hrtimer_cancel,
TP_printk("timer=%p", __entry->timer)
);

+TRACE_EVENT(itimer_state,
+
+ TP_PROTO(int which, struct itimerval *value, cputime_t expires),
+
+ TP_ARGS(which, value, expires),
+
+ TP_STRUCT__entry(
+ __field( int, which )
+ __field( cputime_t, expires )
+ __field( long, value_sec )
+ __field( long, value_usec )
+ __field( long, interval_sec )
+ __field( long, interval_usec )
+ ),
+
+ TP_fast_assign(
+ __entry->which = which;
+ __entry->expires = 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;
+ ),
+
+ TP_printk("which=%d expires=%lu it_value=%lu.%lu it_interval=%lu.%lu",
+ __entry->which, __entry->expires,
+ __entry->value_sec, __entry->value_usec,
+ __entry->interval_sec, __entry->interval_usec)
+);
+
+TRACE_EVENT(itimer_expire,
+
+ TP_PROTO(int which, struct pid *pid, cputime_t now),
+
+ TP_ARGS(which, pid, now),
+
+ TP_STRUCT__entry(
+ __field( int , which )
+ __field( int, pid )
+ __field( cputime_t, now )
+ ),
+
+ TP_fast_assign(
+ __entry->which = which;
+ __entry->now = now;
+ __entry->pid = pid_vnr(pid);
+ ),
+
+ TP_printk("pid=%d which=%d now=%lu", __entry->pid, __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..7e9ee89 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, sig->leader_pid, 0);
kill_pid_info(SIGALRM, SEND_SIG_PRIV, sig->leader_pid);

return HRTIMER_NORESTART;
@@ -139,7 +141,7 @@ int do_setitimer(int which, struct itimerval *value, struct itimerval *ovalue)
struct task_struct *tsk = current;
struct hrtimer *timer;
ktime_t expires;
- cputime_t cval, cinterval, nval, ninterval;
+ cputime_t cval, cinterval, nval = 0, ninterval;

/*
* Validate the timevals in value.
@@ -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..63e93bf 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, sig->leader_pid, 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, sig->leader_pid, utime);
__group_send_sig_info(SIGVTALRM, SEND_SIG_PRIV, tsk);
}
if (!cputime_eq(sig->it_virt_expires, cputime_zero) &&
--
1.6.1.2



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