On Wed, Apr 04, 2018 at 10:47:06AM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> > > In order to address the issue with short idle duration predictions > by the idle governor after the scheduler tick has been stopped, > reorder the code in cpuidle_idle_call() so that the governor idle > state selection runs before tick_nohz_idle_go_idle() and use the > "nohz" hint returned by cpuidle_select() to decide whether or not > to stop the tick. > > This isn't straightforward, because menu_select() invokes > tick_nohz_get_sleep_length() to get the time to the next timer > event and the number returned by the latter comes from > __tick_nohz_idle_stop_tick(). Fortunately, however, it is possible > to compute that number without actually stopping the tick and with > the help of the existing code. > > Namely, tick_nohz_get_sleep_length() can be made call > tick_nohz_next_event(), introduced earlier, to get the time to the > next non-highres timer event. If that happens, tick_nohz_next_event() > need not be called by __tick_nohz_idle_stop_tick() again. > > If it turns out that the scheduler tick cannot be stopped going > forward or the next timer event is too close for the tick to be > stopped, tick_nohz_get_sleep_length() can simply return the time to > the next event currently programmed into the corresponding clock > event device. > > In addition to knowing the return value of tick_nohz_next_event(), > however, tick_nohz_get_sleep_length() needs to know the time to the > next highres timer event, but with the scheduler tick timer excluded, > which can be computed with the help of hrtimer_get_next_event(). > > That minimum of that number and the tick_nohz_next_event() return > value is the total time to the next timer event with the assumption > that the tick will be stopped. It can be returned to the idle > governor which can use it for predicting idle duration (under the > assumption that the tick will be stopped) and deciding whether or > not it makes sense to stop the tick before putting the CPU into the > selected idle state. > > With the above, the sleep_length field in struct tick_sched is not > necessary any more, so drop it. > > Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com>
Reviewed-by: Frederic Weisbecker <frede...@kernel.org>