Messages in this thread |  | | From | "Rafael J. Wysocki" <> | Date | Thu, 4 Oct 2018 19:11:44 +0200 | Subject | Re: [PATCH 5/6] cpuidle: menu: Avoid computations for very close timers |
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On Thu, Oct 4, 2018 at 5:50 PM Daniel Lezcano <daniel.lezcano@linaro.org> wrote: > > On Tue, Oct 02, 2018 at 11:46:28PM +0200, Rafael J. Wysocki wrote: > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > > > If the next timer event (with the tick excluded) is closer than the > > target residency of the second state or the PM QoS latency constraint > > is below its exit latency, state[0] will be used regardless of any > > other factors, so skip the computations in menu_select() then and > > return 0 straight away from it. > > > > Still, do that after the bucket has been determined to avoid > > disturbing the wakeup statistics in general. > > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> > > --- > > drivers/cpuidle/governors/menu.c | 12 ++++++++++++ > > 1 file changed, 12 insertions(+) > > > > Index: linux-pm/drivers/cpuidle/governors/menu.c > > =================================================================== > > --- linux-pm.orig/drivers/cpuidle/governors/menu.c > > +++ linux-pm/drivers/cpuidle/governors/menu.c > > @@ -309,6 +309,18 @@ static int menu_select(struct cpuidle_dr > > get_iowait_load(&nr_iowaiters, &cpu_load); > > data->bucket = which_bucket(data->next_timer_us, nr_iowaiters); > > > > + if (unlikely(drv->state_count <= 1) || > > I'm not sure this test is necessary.
Yes, it is IMO.
Strictly speaking it prevents state[1] from being accessed if the count is not 2 at least.
> If state_count == 0, we don't have to select anything as the cpuidle can't register because of: > > static int __cpuidle_register_driver(struct cpuidle_driver *drv) > { > int ret; > > if (!drv || !drv->state_count) > return -EINVAL; > > [ ... ] > } > > If state_count == 1, then there is nothing to select, it is always the state 0.
Which is why it is better to simply return 0 right away in this case. :-)
I guess I could compare state_count just to 1, but <= 1 works too.
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