• Rafael J. Wysocki's avatar
    cpuidle: Return nohz hint from cpuidle_select() · 45f1ff59
    Rafael J. Wysocki authored
    Add a new pointer argument to cpuidle_select() and to the ->select
    cpuidle governor callback to allow a boolean value indicating
    whether or not the tick should be stopped before entering the
    selected state to be returned from there.
    
    Make the ladder governor ignore that pointer (to preserve its
    current behavior) and make the menu governor return 'false" through
    it if:
     (1) the idle exit latency is constrained at 0, or
     (2) the selected state is a polling one, or
     (3) the expected idle period duration is within the tick period
         range.
    
    In addition to that, the correction factor computations in the menu
    governor need to take the possibility that the tick may not be
    stopped into account to avoid artificially small correction factor
    values.  To that end, add a mechanism to record tick wakeups, as
    suggested by Peter Zijlstra, and use it to modify the menu_update()
    behavior when tick wakeup occurs.  Namely, if the CPU is woken up by
    the tick and the return value of tick_nohz_get_sleep_length() is not
    within the tick boundary, the predicted idle duration is likely too
    short, so make menu_update() try to compensate for that by updating
    the governor statistics as though the CPU was idle for a long time.
    
    Since the value returned through the new argument pointer of
    cpuidle_select() is not used by its caller yet, this change by
    itself is not expected to alter the functionality of the code.
    Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    45f1ff59
ladder.c 5.55 KB