Bugs in Round Robin ??

Bugs in Round Robin ??

[Philippe.LAFFONT]

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     I currently experiment some problem with the Round Robin policy that 
     doesn't seem to work in V2.2.13 . 
     In RR each process should have the same time slice for its own 
     execution ie should have acces to the processor for (almost) the same 
     period of time. Thus each process should progress in the same way 
     (assuming that none of them is blocked on semaphores, queues...). 
     However this is not the behavior I got : it seems some process 
     monopolize the CPU almost untill their completion causing the other 
     processes to be starved
     
     
     To illustrate this issue I made the following test:
     
     I launched 10 times the same program with priority 10 of Round Robin 
     policy (from a shell having priority 20 of FIFO policy). Each program 
     does an infinite busy loop (while (1)).
     One minute later, I launched the "ps" command and I was expected that 
     the TIME values of all these processes are in an interval which is T 
     large, where T is given by sched_rr_get_interval() i.e. T=150ms in 
     this release.
     
     But the ps result was:
     
     PID TTY          TIME CMD
     652 tty1     00:00:00 login
     1549 tty1     00:00:00 bash
     1566 tty1     00:00:00 bash
     1596 tty1     00:01:12 my_program
     1597 tty1     00:00:02 my_program
     1598 tty1     00:00:01 my_program
     1599 tty1     00:00:01 my_program
     1600 tty1     00:00:05 my_program
     1601 tty1     00:00:01 my_program
     1602 tty1     00:00:00 my_program
     1603 tty1     00:00:16 my_program
     1604 tty1     00:00:01 my_program
     1605 tty1     00:00:00 my_program
     1610 tty1     00:00:00 ps
     
     
     Does someone have any explanation of this behavior? 
     
     
     Thanks in advance.