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: 1. I think there is no WHY, but this probably can be patched if we deem it as a problem. 2. 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. > 2. Why the scheduler only pick up Task B as heir task? > 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(); > 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! > _______________________________________________ > 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. > > <http://lists.rtems.org/mailman/listinfo/users>
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