RTEMS Sporadic Server BUG or FEATURE?

[Alex]

Hello,

Suppose a program with the single POSIX thread (main) using the SCHED_SPORADIC policy.

When specifying the following properties:

...
scparam.ss_replenish_period.tv_sec=1
scparam.ss_replenish_period.tv_nsec=500000000
scparam.ss_initial_budget.tv_sec=1
scparam.ss_initial_budget.tv_nsec=250000000
scparam.sched_priority=254
scparam.ss_low_priority=252
...


one hopes that the thread will execute for 1,25 seconds in 254 priority, right?
As there is only one thread, next the thread will execute during a 1,5 seconds with priority 252.
Is this right?


while(1)
{
   "print pthread_getschedparam(...).priority"
}


When I execute the test program what I see is that the thread executes 1,25 seconds in the 254 priority and 
a few instants (< 0,5 seconds) in the 252 priority.
Why the thread doens't executes all the replenish period in the 252 priority?



Next, I tried to change the properties like this:


...
scparam.ss_replenish_period.tv_sec=3
scparam.ss_replenish_period.tv_nsec=500000000
scparam.ss_initial_budget.tv_sec=1
scparam.ss_initial_budget.tv_nsec=250000000
scparam.sched_priority=254
scparam.ss_low_priority=252
...


Executing the program I see that the thread executes about one second in 
254 priority and about 3 seconds in the 252 priority. Good.


Next, I tried to change the properties like this:


...
scparam.ss_replenish_period.tv_sec=5
scparam.ss_replenish_period.tv_nsec=500000000
scparam.ss_initial_budget.tv_sec=1
scparam.ss_initial_budget.tv_nsec=250000000
scparam.sched_priority=254
scparam.ss_low_priority=252
...


Executing the program I see that the thread executes about one second in 
254 priority and about 5 seconds in the 252 priority.Good.

 
Conclusion, it seems like the specified replenish period must always be  > 2*budget  ?!

Is this the normal behaviour of the SPORADIC Server?


In all tests I used the following configuration:

...
#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
...
#define CONFIGURE_MICROSECONDS_PER_TICK 1000
#define CONFIGURE_TICKS_PER_TIMESLICE   1
...



Thank you for your attention,

Alex




Here is the complete test source code (based on rtems samples):


#define CONFIGURE_INIT
#include <errno.h>
#include <time.h>
#include <string.h>
#include <sched.h>
#include <stdio.h>
#include <assert.h>
#include <stdlib.h>
#include <rtems.h>
#include <bsp.h>
#include <pthread.h>

#define CONFIGURE_INIT_TASK_ENTRY_POINT   POSIX_Init


pthread_t        Init_id;
pthread_t        Task_id;


void *POSIX_Init(void *argument)
{
  int                  status;
  int                  passes;
  int                  schedpolicy;
  int                  priority;
  struct sched_param   schedparam;

  Init_id = pthread_self();
  printk( "Init's ID is 0x%08x\n", Init_id );

  status = pthread_getschedparam( pthread_self(), &schedpolicy, &schedparam );
  assert( !status );

  priority = schedparam.sched_priority;
  printk(" - current priority = %d", priority );

  schedparam.ss_replenish_period.tv_sec = 5;
  schedparam.ss_replenish_period.tv_nsec = 500000000;
  schedparam.ss_initial_budget.tv_sec = 1;
  schedparam.ss_initial_budget.tv_nsec = 250000000;

  schedparam.sched_priority = 254;
  schedparam.ss_low_priority = 252;


  status = pthread_setschedparam( pthread_self(), SCHED_SPORADIC, &schedparam );
  assert( !status );


  status = pthread_getschedparam( pthread_self(), &schedpolicy, &schedparam );
  assert( !status );

  priority = schedparam.sched_priority;
  printk("\n - new priority = %d", priority );

  /* go into a loop consuming CPU time to watch our priority change */
  for ( passes=0 ; passes <= 9 ; )
  {
    status = pthread_getschedparam( pthread_self(), &schedpolicy, &schedparam );
    assert( !status );

    if ( priority != schedparam.sched_priority )
    {
      priority = schedparam.sched_priority;
      printk("\n new priority = %d", priority );
      passes++;
    }
  }

  exit(0);
}



#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
#define CONFIGURE_MAXIMUM_POSIX_THREADS   2
#define CONFIGURE_MAXIMUM_POSIX_KEYS     10
#define CONFIGURE_MAXIMUM_POSIX_MUTEXES  10
#define CONFIGURE_POSIX_INIT_THREAD_TABLE

#define CONFIGURE_MICROSECONDS_PER_TICK 	1000
#define CONFIGURE_TICKS_PER_TIMESLICE   	1

#include <confdefs.h>





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