• Philippe Gerum's avatar
    evl/timer: remove timer priority logic · 8d544b48
    Philippe Gerum authored
    
    
    Prioritization of timers in timer queues dates back to the Dark Ages
    of Xenomai 2.x, when multiple time bases would co-exist in the core,
    some of which representing date values as a count of periodic ticks.
    In such a case, multiple timers might elapse on the very same tick,
    hence the need for prioritizing them.
    
    With a single time base indexing timers on absolute date values, which
    are expressed as a 64bit monotonic count of nanoseconds, the
    likelihood of observing identical trigger dates is very low.
    
    Furthermore, the formerly defined priorities where assigned as
    follows:
    
    1) high priority to the per-thread periodic and resource timers
    2) medium priority to the user-defined timers
    3) low priority to the in-band tick emulation timer
    
    It turns out that forcibly prioritizing 1) over 2) is at least
    debatable, if not questionable: resource timers have no high priority
    at all, they merely tick on the (unlikely) timeout condition. On the
    other hand, user-defined timers may well deal with high priority
    events only some EVL driver code may know about.
    
    Finally, handling 3) is a fast operation on top of Dovetail, which is
    already deferred internally whenever the timer management core detects
    that some oob activity is running/pending.
    
    So we may remove the logic handling the timer priority, only relying
    on the trigger date for dispatching. This should save precious cycles
    in the hot path without any actual downside.
    Signed-off-by: default avatarPhilippe Gerum <rpm@xenomai.org>
    8d544b48
thread.c 66.9 KB