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List:       linux-pm
Subject:    Re: [RFC/RFT][PATCH v6] cpuidle: New timer events oriented governor for tickless systems
From:       "Rafael J. Wysocki" <rafael () kernel ! org>
Date:       2018-11-30 8:51:19
Message-ID: CAJZ5v0j6AEjztoFfpQAc3NgQ5JtsWgRqscoE_u1eespVM-Cnmw () mail ! gmail ! com
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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.

> 
> @@ -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!


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