Re: [RFC/RFT][PATCH v6] cpuidle: New timer events oriented governor for tickless systems

Rafael J. Wysocki
2018-12-03T23:47:55Z

On Friday, November 30, 2018 9:51:19 AM CET Rafael J. Wysocki wrote:
> Hi Doug,
>
> On Fri, Nov 30, 2018 at 8:49 AM Doug Smythies <dsmythies@telus.net> wrote:
> >
> > Hi Rafael,
> >
> > On 2018.11.23 02:36 Rafael J. Wysocki wrote:
> >
> > ... [snip]...
> >
> > > +/**
> > > + * teo_find_shallower_state - Find shallower idle state matching given duration.
> > > + * @drv: cpuidle driver containing state data.
> > > + * @dev: Target CPU.
> > > + * @state_idx: Index of the capping idle state.
> > > + * @duration_us: Idle duration value to match.
> > > + */
> > > +static int teo_find_shallower_state(struct cpuidle_driver *drv,
> > > + struct cpuidle_device *dev, int state_idx,
> > > + unsigned int duration_us)
> > > +{
> > > + int i;
> > > +
> > > + for (i = state_idx - 1; i > 0; i--) {
> > > + if (drv->states[i].disabled || dev->states_usage[i].disable)
> > > + continue;
> > > +
> > > + if (drv->states[i].target_residency <= duration_us)
> > > + break;
> > > + }
> > > + return i;
> > > +}
> >
> > I think this subroutine has a problem when idle state 0
> > is disabled.
>
> You are right, thanks!
>
> > Perhaps something like this might help:
> >
> > diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
> > index bc1c9a2..5b97639 100644
> > --- a/drivers/cpuidle/governors/teo.c
> > +++ b/drivers/cpuidle/governors/teo.c
> > @@ -196,7 +196,8 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
> > }
> >
> > /**
> > - * teo_find_shallower_state - Find shallower idle state matching given duration.
> > + * teo_find_shallower_state - Find shallower idle state matching given
> > + * duration, if possible.
> > * @drv: cpuidle driver containing state data.
> > * @dev: Target CPU.
> > * @state_idx: Index of the capping idle state.
> > @@ -208,13 +209,15 @@ static int teo_find_shallower_state(struct cpuidle_driver *drv,
> > {
> > int i;
> >
> > - for (i = state_idx - 1; i > 0; i--) {
> > + for (i = state_idx - 1; i >= 0; i--) {
> > if (drv->states[i].disabled || dev->states_usage[i].disable)
> > continue;
> >
> > if (drv->states[i].target_residency <= duration_us)
> > break;
> > }
> > + if (i < 0)
> > + i = state_idx;
> > return i;
> > }
>
> I'll do something slightly similar, but equivalent.

I actually ended up fixing it differently, as the above will cause state_idx
to be returned even if some states shallower than state_idx are enabled, but
their target residencies are higher than duration_us. In that case, though,
it still is more correct to return the shallowest enabled state rather than
state_idx.

> >
> > @@ -264,7 +267,6 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
> > if (max_early_idx >= 0 &&
> > count < cpu_data->states[i].early_hits)
> > count = cpu_data->states[i].early_hits;
> > -
> > continue;
> > }
> >
> > There is an additional issue where if idle state 0 is disabled (with the above suggested code patch),
> > idle state usage seems to fall to deeper states than idle state 1.
> > This is not the expected behaviour.
>
> No, it isn't.
>
> > Kernel 4.20-rc3 works as expected.
> > I have not figured this issue out yet, in the code.
> >
> > Example (1 minute per sample. Number of entries/exits per state):
> > State 0 State 1 State 2 State 3 State 4 Watts
> > 28235143, 83, 26, 17, 837, 64.900
> > 5583238, 657079, 5884941, 8498552, 30986831, 62.433 << Transition sample, after idle state 0 disabled
> > 0, 793517, 7186099, 10559878, 38485721, 61.900 << ?? should have all gone into Idle state 1
> > 0, 795414, 7340703, 10553117, 38513456, 62.050
> > 0, 807028, 7288195, 10574113, 38523524, 62.167
> > 0, 814983, 7403534, 10575108, 38571228, 62.167
> > 0, 838302, 7747127, 10552289, 38556054, 62.183
> > 9664999, 544473, 4914512, 6942037, 25295361, 63.633 << Transition sample, after idle state 0 enabled
> > 27893504, 96, 40, 9, 912, 66.500
> > 26556343, 83, 29, 7, 814, 66.683
> > 27929227, 64, 20, 10, 931, 66.683
>
> I see.
>
> OK, I'll look into this too, thanks!

This probably is the artifact of the fix for the teo_find_shallower_state()
issue.

Anyway, I'm not able to reproduce this with the teo_find_shallower_state() issue
fixed differently.

Thanks,
Rafael