• John Blackwood's avatar
    sched: fix sched_rt_rq_enqueue() resched idle · f3ade837
    John Blackwood authored
    When sysctl_sched_rt_runtime is set to something other than -1 and the
    CONFIG_RT_GROUP_SCHED kernel parameter is NOT enabled, we get into a state
    where we see one or more CPUs idling forvever even though there are
    real-time
    tasks in their rt runqueue that are able to run (no longer throttled).
    
    The sequence is:
    
    - A real-time task is running when the timer sets the rt runqueue
        to throttled, and the rt task is resched_task()ed and switched
        out, and idle is switched in since there are no non-rt tasks to
        run on that cpu.
    
    - Eventually the do_sched_rt_period_timer() runs and un-throttles
        the rt runqueue, but we just exit the timer interrupt and go back
        to executing the idle task in the idle loop forever.
    
    If we change the sched_rt_rq_enqueue() routine to use some of the code
    from the CONFIG_RT_GROUP_SCHED enabled version of this same routine and
    resched_task() the currently executing task (idle in our case) if it is
    a lower priority task than the higher rt task in the now un-throttled
    runqueue, the problem is no longer observed.
    Signed-off-by: default avatarJohn Blackwood <john.blackwood@ccur.com>
    Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    f3ade837
sched_rt.c 34.3 KB