Timeslicing question

Kenneth Peters Kenneth.J.Peters at jpl.nasa.gov
Fri Oct 3 18:00:54 UTC 2003

My tasks are truly preemptible and timeslicing. I had already used a
modified CPU_usage_Dump() function from the RTEMS-4.5.0 libmisc directory
to print out the is_preemptible and budget_algorithm parameters (among
others). Also, I used the rtems_task_switch_extension to log information at
every task switch so I could see which tasks were executing and how their
cpu_time_budgets were behaving.

What I have done as a quick fix is to take a copy of the Classic API
rtems_task_mode() function and modify it to

rtems_status_code my_rtems_task_mode(
   rtems_mode mode_set,
   rtems_mode mask,
   rtems_mode *previous_mode_set,
   boolean use_timeslice_exhaustion,
   boolean *previous_use_timeslice_exhaustion

and adjust the code appropriately so that a task can set itself to, in
effect, use the SCHED_RR methodology. The basic code is

if ( mask & RTEMS_TIMESLICE_MASK ) {
   if ( _Modes_is_timeslice(mode_set) ) {
     if (use_timeslice_exhaustion) {
     } else {
   } else {

This does make my tasks act as I desired. (Actually I also set
executing->Start.budget_algorithm since my tasks are sometimes restarted
and I don't want that to risk getting a task stuck again.)

Now I have to judge whether I should use this hack, or convert to POSIX
task startup (possibly non-trivial due to things elsewhere in the code like
looking tasks up by name), or change the way my tasks work so that they can
do their jobs under the standard Classic API timeslicing method. But that's
my job.

Thanks for the help,

At 05:34 PM 10/2/2003 -0700, Kamen Penev wrote:
 >Kenneth Peters wrote:
 >>Ugh. Thanks for the quick reply. This is ugly, though, if I have to go
 >>through and retrofit my task functions to the POSIX API.
 >It is not that much work really. Follow the example that I gave at the end
 >of the second thread. You don't have to change all your tasks to POSIX.
 >Only the ones that need SCHED_RR. And you can still use classic
 >semaphores, message queues etc. inside them.
 >>Joel indicated maybe the pthread_setschedparam() function could be called
 >>on a Classic API task to tweak the budget_algorithm parameter. If that
 >>value is really the only thing I need to change, that would be a better
 >>way for me. Has anyone tried that?
 >It didn't work for me back then, as reported in:
 >The bug may have been fixed, I don't know. Try pthread_setschedparam and
 >see what happens.

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