Thank you for your reply!
To Kuan-Hsun Chen:
This is my test eviroment and test case:
Test eviroment:
rtems-bsp: arm/xilinx_zynq_a9_qemu
rtems version: 5.1
Test case:
#include <rtems.h>
#include <stdlib.h>
#include <stdio.h>
rtems_id Task[3];
static void taskRunner(rtems_task_argument arg)
{
while(1)
{
if (arg == 2)
{
rtems_task_wake_after(1);
}
printk("task TST%d running\n",arg);
}
}
rtems_task Init(
rtems_task_argument ignored
)
{
rtems_status_code ret = rtems_task_create(rtems_build_name('T', 'S',
'T', '0'), 128, RTEMS_MINIMUM_STACK_SIZE,
RTEMS_TIMESLICE | RTEMS_PREEMPT , RTEMS_LOCAL,
&Task[0]);
ret = rtems_task_create(rtems_build_name('T', 'S', 'T', '1'), 128,
RTEMS_MINIMUM_STACK_SIZE,
RTEMS_TIMESLICE | RTEMS_PREEMPT , RTEMS_LOCAL, &Task[1]);
ret = rtems_task_create(rtems_build_name('T', 'S', 'T', '2'), 2,
RTEMS_MINIMUM_STACK_SIZE,
RTEMS_TIMESLICE | RTEMS_PREEMPT , RTEMS_LOCAL, &Task[2]);
ret = rtems_task_start(Task[0], taskRunner,0);
ret = rtems_task_start(Task[1], taskRunner,1);
ret = rtems_task_start(Task[2], taskRunner,2);
rtems_task_exit();
}
To Gedare Bloom:
It works only when pthread_setschedparam() with SCHED_RR was called after
rtems_task_start().
And when call rtems_task_mode() or rtems_task_restart(), the same problem
will appears again, seems that SCHED_RR flag was cleaned away.
Regards
Wang
"Gedare Bloom" <ged...@rtems.org> 2021/06/10 22:24:51:
> On Thu, Jun 10, 2021 at 4:10 AM Kuan-Hsun Chen <c00...@gmail.com> wrote:
> >
> > Hello,
> >
> > If that is the case, I think we should probably first agree on,
> what is the preferred behavior under the circumstance. I think
> picking heir tasks always in the same order is a proper design, but
> the preemption should not corrupt the "fair" time slicing in my
> opinion (so follow what you observe). From what I can find in the
> documents or source code, e.g.,
> >
> > https://docs.rtems.org/branches/master/c-user/task/
> background.html?highlight=slice#task-priority (the latest version)
> > https://docs.rtems.org/releases/rtemsdocs-4.6.2/share/rtems/html/
> c_user/c_user00303.html (old version)
> > https://github.com/RTEMS/rtems/blob/master/cpukit/include/rtems/
> rtems/tasks.h
> >
> > There is no definition or clarification about the problem you
> mentioned. To answer some of your questions:
> >
> > I think there is no WHY, but this probably can be patched if we
> deem it as a problem.
> > Timeslicing in RTOS usually follows a round-robin manner according
> to an given order. To have a determinate behavior, I think it makes
> sense that it always pick Task B as heir task.
> >
> > Could you provide your testing code so that we can repeat the same
> scenario? I would like to give a try as well.
> >
> > Best regards,
> > Kuan-Hsun
> >
> >
> > On Thu, Jun 10, 2021 at 11:25 AM <wangqia...@sugon.com> wrote:
> >>
> >> Description of the issue：
> >> I created three tasks, Task A, Task B and Task C. All tasks are
> based on RTEMS_TIMESLICE | RTEMS_PREEMPT , Task A has a higher
> priority than other tasks, Task B has the same priority as Task C.
> >> Tasks B and C loop forever, Task A sleeps 1 TICK on an endless
> loop. When I test, I find that task C is not scheduled.
> >>
> >> Hope result:
> >> I was expecting tasks A, B, and C to be scheduled. Task A can
> preempt task B and C. Tasks B and C can switch to each other when
> the time slice runs out.
> >>
> >> Actual result:
> >> When task A preempts task B and run out its timeslice, then
> switch to task B, task B's timeslice will reset to
> _Watchdog_Ticks_per_timeslice.
> >> While the task B is still running, Task A preempts task B again.
> Task A will pick up task B as heir task and reset task B's timeslice.
> >> This will cause task C never be scheduled.
> >>
> >> My doubts ：
> >> 1. Why must reset the time slice every time when switch tasks.
> Because THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE is set.
>
> >> 2. Why the scheduler only pick up Task B as heir task?
> The timeslice never exhausts, and the task never yields.
>
> >> 3. Can I comment the following code in _Thread_Do_dispatch()? Is
> there any problem if I change it this way?
> >> if ( heir->budget_algorithm ==
> THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE )
> >> heir->cpu_time_budget =
> rtems_configuration_get_ticks_per_timeslice();
>
> No, this breaks THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE
>
> >> 4. I found that only in POSIX can I use the algorithm
> THREAD_CPU_BUDGET_ALGORITHM_EXHAUST_TIMESLICE , RTEMS classics api
> only can use THREAD_CPU_BUDGET_ALGORITHM_RESET_TIMESLICE.
> >> Can I use THREAD_CPU_BUDGET_ALGORITHM_EXHAUST_TIMESLICE in
> RTEMS classics api.nd rtems_task_mode.
> >> 5. Can anyone give some suggestions to solve the problem? thanks!
>
> Classic and POSIX APIs can be mixed. It is a poorly documented benefit
> of RTEMS. I think in this case, you should be able to use
> pthread_setschedparam(...) with passing policy == SCHED_RR to get the
> behavior you seek. You have to use posix priorities in the sched_param
> argument. though, or else your thread will have its priority changed.
> Pass the task_id instead of pthread_t as the first argument, and the
> rest should work itself out. Do let us know if that works or it
> doesn't work/you have more questions.
>
> Gedare
>
> >> _______________________________________________
> >> users mailing list
> >> users@rtems.org
> >> http://lists.rtems.org/mailman/listinfo/users
> >>
> >> --
> >> Diese Mail wurde mobil geschrieben. Etwaige Rechtschreibfehler
> sind volle Absicht und als großzügiges Geschenk zu verstehen.
> >>
> >
> > _______________________________________________
> > users mailing list
> > users@rtems.org
> > http://lists.rtems.org/mailman/listinfo/users
_______________________________________________
users mailing list
users@rtems.org
http://lists.rtems.org/mailman/listinfo/users
