On Wed, 27 Feb 2019 at 00:41, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > On Wed, Feb 27, 2019 at 12:16 AM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > > > > On Tue, 26 Feb 2019 at 23:08, Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > > > > > On Tue, Feb 26, 2019 at 3:54 PM Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote: > > > > > > > > A common piece of data used by cpuidle governors, is the information about > > > > when the next timer/tick is going to fire. Rather than having each governor > > > > calling tick_nohz_get_next_timer|hrtimer() separately, let's consolidate > > > > the code by calling these functions before invoking the ->select() callback > > > > of the governor - and store the output data in the struct cpuidle_device. > > > > > > That misses the point IMO. > > > > > > You don't need to store two values in struct cpuidle_device, but just > > > one, and not before running ->select(), but before invoking the > > > driver's ->enter() callback. > > > > Okay! Thanks for letting me know! > > > > > > > > At that point, the decision on whether or not to stop the scheduler > > > tick has been made already and it should be sufficient to store the > > > return value of tick_nohz_get_next_hrtimer() introduced by patch > > > [3/8], because that value represents the next timer regardless of what > > > has been decided with respect to the tick. > > > > Just to make sure I get this correctly, because it seems like I have > > missed a few points here.... > > > > If we decided to keep the tick running, then > > tick_nohz_get_next_hrtimer() gives the next tick or the next hrtimer, > > whatever that comes first. There are no other timer that can expire > > earlier than this, right!? > > > > If we decided to stop the tick, then tick_nohz_get_next_hrtimer() will > > give us the next hrtimer. Again, then there are no other timer that > > can't expire earlier than this, right!? > > Right in both cases. > > IOW, that is the event that will wake up the CPU unless any other > (non-timer) interrupts (or equivalent events) occur in the meantime. > > > > > > > And you won't need the tick_nohz_get_next_timer() any more then. > > > > Alright, this kind of brings this hole thing back closer to v10 - and > > then we should stick to use tick_nohz_get_sleep_length() as is for the > > cpuidle governors. That is what you are saying? > > For the menu and teo governors - yes. IMO > tick_nohz_get_sleep_length() is as good as it gets in there. Okay, got it! Thanks for your helpful answers! I will post a v12 as soon as I can, so we can look into the other parts of the series. Kind regards Uffe
