Re: [Xenomai-main] Modification scheduler XENOMAI

[Philippe Gerum]

address@hidden wrote:
 > Selon Philippe Gerum <address@hidden>:
 > 
 > > address@hidden wrote:
 > >  > Hi all,
 > >  > 
 > >  > We are using XENOMAI on top of POSIX, we're using it for avionic OS
 > > emulation.
 > >  > Our first tests make us very enthousiam.
 > >  > 
 > >  > But the OS we have to emulate is a little special, it is base on a 
 > > concept
 > > of
 > >  > partitionning, a partition is a set of process, and these partition are
 > > serially
 > >  > scheduled. and  within each partition processes are schedule "normaly"
 > >  > eg:
 > >  > 
 > >  >
 > > |_____PART1______|___PART2___|_PART3_||_____PART1______|___PART2___|_PART3_|
 > > 
 > >  > etc .....
 > >  > 
 > >  > with some process in PART1, some other in PART2 etc....
 > > 
 > > Arinc653?
 > Yes it is derived from this.
 > 
 > And the partitionning is really a problem for us... 
 > We want to make changes as clean as possible, but the scheduler doesn't seem 
 > to
 > be prepared for this.... and the difficulty is to not break Xenomai 
 > abstraction.
 > 
 > Our first idea was to play with the scheduler hook, but we can do nothing
 > interesting with this.

Provided the number of processes is bound and relatively small into
these partitions (IIRC, it costs about 100-150ns to suspend a
non-current thread on a mid-range Celeron), maybe you could use a
specialized Xenomai thread with a higher priority than any other
process acting as the timeframe scheduler?

This would look this this:

     void timeframe_sched (void) {

     for (;;) {
          xnpod_delay(ticks_to_next_partition);
          foreach (threads in runqueue[current_part_id]) {
             xnpod_suspend_thread(thread,XNSLICE,XN_INFINITE,NULL,NULL);
          }
          foreach (threads in runqueue[next_part_id]) {
             xnpod_resume_thread(thread,XNSLICE);
          }
     }

The XNSLICE flag does not exist yet, but you could define it using a
spare bit from thread.h, and add it to the XNTHREAD_BLOCK_BITS
mask. NOTE: do not use XNSUSP for this purpose, otherwise you would
get brain-damage conflicts with synchronization objects which use it.

Philippe.