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
