Messages in this thread Patch in this message | | | Date | Mon, 29 Apr 2013 02:25:34 -0400 | From | KOSAKI Motohiro <> | Subject | Re: [PATCH v2 3/3] process cputimer is moving faster than its corresponding clock |
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(4/27/13 12:41 AM), Olivier Langlois wrote: > > > Add thread group delta to cpu timer sample when computing a timer expiration. > > This is mandatory to make sure that the posix cpu timer does not fire too > soon relative to the process cpu clock which do include the task group delta. > > test case to validate the patch is glibc-2.17/rt/tst-cputimer1.c
First, I could reproduce this issue. thanks. Second, actually, this issue is not cause by race. This just occur by timer initialization mistake. I'll show you the smallest fix.
> @@ -697,7 +755,8 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int flags, > if (CPUCLOCK_PERTHREAD(timer->it_clock)) { > cpu_clock_sample(timer->it_clock, p, &val); > } else { > - cpu_timer_sample_group(timer->it_clock, p, &val); > + cpu_timer_sample_group(timer->it_clock, p, &val, > + CPUTIMER_NEED_DELTA);
POSIX says,
http://pubs.opengroup.org/onlinepubs/7908799/xsh/timer_gettime.html > If the argument ovalue is not NULL, the function timer_settime() stores, > in the location referenced by ovalue, a value representing the previous > amount of time before the timer would have expired or zero if the timer > was disarmed, together with the previous timer reload value. The members > of ovalue are subject to the resolution of the timer, and they are the > same values that would be returned by a timer_gettime() call at that point in time. ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
but your posix_cpu_timer_set() and posix_cpu_timer_get() are not consistent. I'm worry about this.
> } > > if (old) { > @@ -845,7 +904,8 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec *itp) > read_unlock(&tasklist_lock); > goto dead; > } else { > - cpu_timer_sample_group(timer->it_clock, p, &now); > + cpu_timer_sample_group(timer->it_clock, p, &now, > + CPUTIMER_NO_DELTA); > > clear_dead = (unlikely(p->exit_state) && > thread_group_empty(p)); > }
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