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

From: Nicholas Piggin <[email-masked]>
Date: Tue, 30 May 2017 21:10:06 +1000

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

> 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.

Looks like mpe has merged this in next now. I just wonder if this
particular bit would be relevant for POWER8 and therefore be a
stable candidate? All the POWER9 idle fixes may not be suitable for
stable.

> > > 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.

Okay that makes sense, thanks for explaining.

Since your patches are now merged, it's a matter of preference,
if you want to send any cleanup patches you can take any of my
suggestions.

Thanks for the fixes!