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    SubjectRe: [PATCH v2 1/3] process cputimer is moving faster than its corresponding clock
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    On Mon, 2013-04-29 at 15:09 -0400, KOSAKI Motohiro wrote:
    > (4/29/13 2:54 PM), Olivier Langlois wrote:
    > > On Mon, 2013-04-29 at 14:31 -0400, KOSAKI Motohiro wrote:
    > >> (4/29/13 2:20 PM), Olivier Langlois wrote:
    > >>>
    > >>>>
    > >>>>>> I'm confused. glibc's rt/tst-cputimer1 doesn't have thread exiting code. I have
    > >>>>>> no seen any issue in this accounting.
    > >>>>>
    > >>>>> glibc launch a helper thread to receive timer signal and will also
    > >>>>> create a new thread upon signal reception when a timer is created with
    > >>>>> sigev_notify = SIGEV_THREAD;
    > >>>>>
    > >>>>> please see:
    > >>>>>
    > >>>>> glibc-2.17/nptl/sysdeps/unix/sysv/linux/timer_create.c
    > >>>>> glibc-2.17/nptl/sysdeps/unix/sysv/linux/timer_routines.c
    > >>>>
    > >>>> I know. I taled thread exiting. not thread creating. And, as far as I can see, only test sig1 can fail,
    > >>>> not thr[12].
    > >>>>
    > >>> Apart from glibc helper thread, the threads created for handling timer
    > >>> firing all do exit immediatly as soon as user callback returns.
    > >>
    > >> And, libc ensure its exiting finished before starting actual tests. Why such thread exiting
    > >> affect timers code? It shouldn't. becuase signal.cputimer is initialized timer_settime().
    > >> The initialization is incorrect, we should fix initialization.
    > >
    > > It doesn't have anything to do with initialisation.
    > >
    > > Quick Quiz #1: How does the cputimer tick?
    > > Answer: With calls to account_group_exec_runtime()
    >
    > Only account when cputimer->running. Quick Quiz: When turn on cputimer->running?
    >
    >
    > > Every task updates occuring after release_task() has been called in
    > > do_exit() (scheduler ticks or the task final schedule() call) will be
    > > lost because tasks stats are added to the global group stats located in
    > > the signal struct in release_task() So every update after release_task()
    > > will be lost but account_group_exec_runtime is still called.
    >
    > tick lost doesn't occur an issue. because glibc only test posix conformance and
    > posix allow inacculacy. In other words, timer must not run faster than real clock.
    > but lost and makes slower are accepted in the test.
    >
    What is lost isn't cputimer tick. They are accounted
    account_group_exec_runtime(). What is lost it is what is added to
    curr->sum_exec_runtime. Thus making the thread group clock running
    slower than the cputimer.

    Please spend some time reading the code and less time writing e-mails.

    Read the code of release_task() and where it is called in do_exit().

    Once it is done, it should be clear to you.




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