Subject: Re: [PATCH 6/6] cpuidle-powernv: Allow Deep stop states that don't stop time

From: Gautham R Shenoy <[email-masked]>
Date: Tue, 30 May 2017 16:20:55 +0530

On Tue, May 30, 2017 at 05:13:57PM +1000, Nicholas Piggin wrote:
> On Tue, 16 May 2017 14:19:48 +0530
> "Gautham R. Shenoy" <[email-masked]> wrote:
> 
> > From: "Gautham R. Shenoy" <[email-masked]>
> > 
> > The current code in the cpuidle-powernv intialization only allows deep
> > stop states (indicated by OPAL_PM_STOP_INST_DEEP) which lose timebase
> > (indicated by OPAL_PM_TIMEBASE_STOP). This assumption goes back to
> > POWER8 time where deep states used to lose the timebase. However, on
> > POWER9, we do have stop states that are deep (they lose hypervisor
> > state) but retain the timebase.
> > 
> > Fix the initialization code in the cpuidle-powernv driver to allow
> > such deep states.
> > 
> > Further, there is a bug in cpuidle-powernv driver with
> > CONFIG_TICK_ONESHOT=n where we end up incrementing the nr_idle_states
> > even if a platform idle state which loses time base was not added to
> > the cpuidle table.
> > 
> > Fix this by ensuring that the nr_idle_states variable gets incremented
> > only when the platform idle state was added to the cpuidle table.
> 
> Should this be a separate patch? Stable?

Ok. Will send it out separately.

> 
> > 
> > Signed-off-by: Gautham R. Shenoy <[email-masked]>
> > ---
> >  drivers/cpuidle/cpuidle-powernv.c | 16 ++++++++++------
> >  1 file changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> > index 12409a5..45eaf06 100644
> > --- a/drivers/cpuidle/cpuidle-powernv.c
> > +++ b/drivers/cpuidle/cpuidle-powernv.c
> > @@ -354,6 +354,7 @@ static int powernv_add_idle_states(void)
> >  
> >  	for (i = 0; i < dt_idle_states; i++) {
> >  		unsigned int exit_latency, target_residency;
> > +		bool stops_timebase = false;
> >  		/*
> >  		 * If an idle state has exit latency beyond
> >  		 * POWERNV_THRESHOLD_LATENCY_NS then don't use it
> > @@ -381,6 +382,9 @@ static int powernv_add_idle_states(void)
> >  			}
> >  		}
> >  
> > +		if (flags[i] & OPAL_PM_TIMEBASE_STOP)
> > +			stops_timebase = true;
> > +
> >  		/*
> >  		 * For nap and fastsleep, use default target_residency
> >  		 * values if f/w does not expose it.
> > @@ -392,8 +396,7 @@ static int powernv_add_idle_states(void)
> >  			add_powernv_state(nr_idle_states, "Nap",
> >  					  CPUIDLE_FLAG_NONE, nap_loop,
> >  					  target_residency, exit_latency, 0, 0);
> > -		} else if ((flags[i] & OPAL_PM_STOP_INST_FAST) &&
> > -				!(flags[i] & OPAL_PM_TIMEBASE_STOP)) {
> > +		} else if (has_stop_states && !stops_timebase) {
> >  			add_powernv_state(nr_idle_states, names[i],
> >  					  CPUIDLE_FLAG_NONE, stop_loop,
> >  					  target_residency, exit_latency,
> > @@ -405,8 +408,8 @@ static int powernv_add_idle_states(void)
> >  		 * within this config dependency check.
> >  		 */
> >  #ifdef CONFIG_TICK_ONESHOT
> > -		if (flags[i] & OPAL_PM_SLEEP_ENABLED ||
> > -			flags[i] & OPAL_PM_SLEEP_ENABLED_ER1) {
> > +		else if (flags[i] & OPAL_PM_SLEEP_ENABLED ||
> > +			 flags[i] & OPAL_PM_SLEEP_ENABLED_ER1) {
> 
> Hmm, seems okay but readability is isn't the best with the ifdef and
> mixing power8 and 9 cases IMO.
> 
> Particularly with the nice regular POWER9 states, we're not doing much
> logic in this loop besides checking for the timebase stop flag, right?
> Would it be clearer if it was changed to something like this (untested
> quick hack)?

Yes, this is very much doable. Some comments below.

> 
> ---
>  drivers/cpuidle/cpuidle-powernv.c | 76 +++++++++++++++++++--------------------
>  1 file changed, 37 insertions(+), 39 deletions(-)
> 
> diff --git a/drivers/cpuidle/cpuidle-powernv.c b/drivers/cpuidle/cpuidle-powernv.c
> index 12409a519cc5..77291389f9ac 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -353,7 +353,9 @@ static int powernv_add_idle_states(void)
>  	}
> 
>  	for (i = 0; i < dt_idle_states; i++) {
> +		unsigned int cpuidle_flags = CPUIDLE_FLAG_NONE;
>  		unsigned int exit_latency, target_residency;
> +
>  		/*
>  		 * If an idle state has exit latency beyond
>  		 * POWERNV_THRESHOLD_LATENCY_NS then don't use it
> @@ -371,6 +373,16 @@ static int powernv_add_idle_states(void)
>  		else
>  			target_residency = 0;
> 
> +		if (flags[i] & OPAL_PM_TIMEBASE_STOP) {
> +			/*
> +			 * All cpuidle states with CPUIDLE_FLAG_TIMER_STOP set
> +			 * depend on CONFIG_TICK_ONESHOT.
> +			 */
> +			if (!IS_ENABLED(CONFIG_TICK_ONESHOT))
> +				continue;
> +			cpuidle_flags = CPUIDLE_FLAG_TIMER_STOP;

Yes, this can be done. We just need to extend this condition to
(flags[i] & OPAL_PM_TIMEBASE_STOP || flags[i] &
OPAL_PM_SLEEP_ENABLED).

Even though all the recent versions of OPAL have OPAL_PM_TIMEBASE_STOP
set for states which have OPAL_PM_SLEEP_ENABLED, I am not sure if
that was always the case and which is why we have the fastsleep case
explicitly coded in the kernel.

> +		}
> +
>  		if (has_stop_states) {
>  			int err = validate_psscr_val_mask(&psscr_val[i],
>  							  &psscr_mask[i],
> @@ -379,50 +391,36 @@ static int powernv_add_idle_states(void)
>  				report_invalid_psscr_val(psscr_val[i], err);
>  				continue;
>  			}
> -		}
> 
> -		/*
> -		 * For nap and fastsleep, use default target_residency
> -		 * values if f/w does not expose it.
> -		 */
> -		if (flags[i] & OPAL_PM_NAP_ENABLED) {
> -			if (!rc)
> -				target_residency = 100;
> -			/* Add NAP state */
> -			add_powernv_state(nr_idle_states, "Nap",
> -					  CPUIDLE_FLAG_NONE, nap_loop,
> -					  target_residency, exit_latency, 0, 0);
> -		} else if ((flags[i] & OPAL_PM_STOP_INST_FAST) &&
> -				!(flags[i] & OPAL_PM_TIMEBASE_STOP)) {
>  			add_powernv_state(nr_idle_states, names[i],
> -					  CPUIDLE_FLAG_NONE, stop_loop,
> -					  target_residency, exit_latency,
> -					  psscr_val[i], psscr_mask[i]);
> -		}
> -
> -		/*
> -		 * All cpuidle states with CPUIDLE_FLAG_TIMER_STOP set must come
> -		 * within this config dependency check.
> -		 */
> -#ifdef CONFIG_TICK_ONESHOT
> -		if (flags[i] & OPAL_PM_SLEEP_ENABLED ||
> -			flags[i] & OPAL_PM_SLEEP_ENABLED_ER1) {
> -			if (!rc)
> -				target_residency = 300000;
> -			/* Add FASTSLEEP state */
> -			add_powernv_state(nr_idle_states, "FastSleep",
> -					  CPUIDLE_FLAG_TIMER_STOP,
> -					  fastsleep_loop,
> -					  target_residency, exit_latency, 0, 0);
> -		} else if ((flags[i] & OPAL_PM_STOP_INST_DEEP) &&
> -				(flags[i] & OPAL_PM_TIMEBASE_STOP)) {
> -			add_powernv_state(nr_idle_states, names[i],
> -					  CPUIDLE_FLAG_TIMER_STOP, stop_loop,
> +					  cpuidle_flags, stop_loop,
>  					  target_residency, exit_latency,
>  					  psscr_val[i], psscr_mask[i]);
> +			nr_idle_states++;
> +		} else {
> +			/*
> +			 * For nap and fastsleep, use default target_residency
> +			 * values if f/w does not expose it.
> +			 */
> +			if (flags[i] & OPAL_PM_NAP_ENABLED) {
> +				if (!rc)
> +					target_residency = 100;
> +				/* Add NAP state */
> +				add_powernv_state(nr_idle_states, "Nap",
> +						  cpuidle_flags, nap_loop,
> +						  target_residency, exit_latency, 0, 0);
> +				nr_idle_states++;
> +			} else if (flags[i] & (OPAL_PM_SLEEP_ENABLED |
> +						OPAL_PM_SLEEP_ENABLED_ER1)) {
> +				if (!rc)
> +					target_residency = 300000;
> +				/* Add FASTSLEEP state */
> +				add_powernv_state(nr_idle_states, "FastSleep",
> +						  cpuidle_flags, fastsleep_loop,
> +						  target_residency, exit_latency, 0, 0);
> +				nr_idle_states++;
> +			}
>  		}
> -#endif
> -		nr_idle_states++;
>  	}
>  out:
>  	return nr_idle_states;
> -- 
> 2.11.0
>