[PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Rafael J. Wysocki]

Hi,

This is a bunch of teo cpuidle governor improvements, some of which are related
to a bug report discussed recently:

https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/

The first patch fixes a bug that may cause an overly deep idle state
to be selected when the scheduler tick has been already stopped.

Patch [2/4] removes an unnecessary function argument.

Patch [3/4] makes teo_update() to use s64 as the data type for its local
variables more consistently.

The last patch reworks the governor's decay implementation to also decay
metric values lower than 8.

Thanks!

[PATCH v1 1/4] cpuidle: governors: teo: Drop incorrect target residency check

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

When the target residency of the current candidate idle state is
greater than the expected time till the closest timer (the sleep
length), it does not matter whether or not the tick has already
been stopped or if it is going to be stopped.  The closest timer
will trigger anyway at its due time, so it does not make sense to
select an idle state with target residency above the sleep length.

Accordingly, drop the teo_state_ok() check done in that case and
let the governor use the teo_find_shallower_state() return value
as the new candidate idle state index.

Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/teo.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
 	 * If the closest expected timer is before the target residency of the
 	 * candidate state, a shallower one needs to be found.
 	 */
-	if (drv->states[idx].target_residency_ns > duration_ns) {
-		i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
-		if (teo_state_ok(i, drv))
-			idx = i;
-	}
+	if (drv->states[idx].target_residency_ns > duration_ns)
+		idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
 
 	/*
 	 * If the selected state's target residency is below the tick length

Re: [PATCH v1 1/4] cpuidle: governors: teo: Drop incorrect target residency check

[Christian Loehle]

On 11/12/25 16:22, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> When the target residency of the current candidate idle state is
> greater than the expected time till the closest timer (the sleep
> length), it does not matter whether or not the tick has already
> been stopped or if it is going to be stopped.  The closest timer
> will trigger anyway at its due time, so it does not make sense to
> select an idle state with target residency above the sleep length.
> 
> Accordingly, drop the teo_state_ok() check done in that case and
> let the governor use the teo_find_shallower_state() return value
> as the new candidate idle state index.
> 
> Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
> Cc: All applicable <stable@vger.kernel.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/cpuidle/governors/teo.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
>  	 * If the closest expected timer is before the target residency of the
>  	 * candidate state, a shallower one needs to be found.
>  	 */
> -	if (drv->states[idx].target_residency_ns > duration_ns) {
> -		i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> -		if (teo_state_ok(i, drv))
> -			idx = i;
> -	}
> +	if (drv->states[idx].target_residency_ns > duration_ns)
> +		idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
>  
>  	/*
>  	 * If the selected state's target residency is below the tick length
> 
> 
> 

AFAICT this check was to not be stuck in a shallow state when tick is already disabled.
There might be a timer armed in t+500us but that might still get cancelled, which
is why we didn't think a below TICK_NSEC 'shallow' state is acceptable?

Re: [PATCH v1 1/4] cpuidle: governors: teo: Drop incorrect target residency check

[Rafael J. Wysocki]

On Thu, Nov 13, 2025 at 12:32 PM Christian Loehle
<christian.loehle@arm.com> wrote:
>
> On 11/12/25 16:22, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > When the target residency of the current candidate idle state is
> > greater than the expected time till the closest timer (the sleep
> > length), it does not matter whether or not the tick has already
> > been stopped or if it is going to be stopped.  The closest timer
> > will trigger anyway at its due time, so it does not make sense to
> > select an idle state with target residency above the sleep length.
> >
> > Accordingly, drop the teo_state_ok() check done in that case and
> > let the governor use the teo_find_shallower_state() return value
> > as the new candidate idle state index.
> >
> > Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
> > Cc: All applicable <stable@vger.kernel.org>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/cpuidle/governors/teo.c |    7 ++-----
> >  1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > --- a/drivers/cpuidle/governors/teo.c
> > +++ b/drivers/cpuidle/governors/teo.c
> > @@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
> >        * If the closest expected timer is before the target residency of the
> >        * candidate state, a shallower one needs to be found.
> >        */
> > -     if (drv->states[idx].target_residency_ns > duration_ns) {
> > -             i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> > -             if (teo_state_ok(i, drv))
> > -                     idx = i;
> > -     }
> > +     if (drv->states[idx].target_residency_ns > duration_ns)
> > +             idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> >
> >       /*
> >        * If the selected state's target residency is below the tick length
> >
> >
> >
>
> AFAICT this check was to not be stuck in a shallow state when tick is already disabled.
> There might be a timer armed in t+500us but that might still get cancelled, which
> is why we didn't think a below TICK_NSEC 'shallow' state is acceptable?

This is all about hrtimers which are not expected to be canceled too
often and real energy is wasted here by going too deep if the timer is
not canceled.

Re: [PATCH v1 1/4] cpuidle: governors: teo: Drop incorrect target residency check

[Rafael J. Wysocki]

On Thu, Nov 13, 2025 at 12:41 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Nov 13, 2025 at 12:32 PM Christian Loehle
> <christian.loehle@arm.com> wrote:
> >
> > On 11/12/25 16:22, Rafael J. Wysocki wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > >
> > > When the target residency of the current candidate idle state is
> > > greater than the expected time till the closest timer (the sleep
> > > length), it does not matter whether or not the tick has already
> > > been stopped or if it is going to be stopped.  The closest timer
> > > will trigger anyway at its due time, so it does not make sense to
> > > select an idle state with target residency above the sleep length.
> > >
> > > Accordingly, drop the teo_state_ok() check done in that case and
> > > let the governor use the teo_find_shallower_state() return value
> > > as the new candidate idle state index.
> > >
> > > Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
> > > Cc: All applicable <stable@vger.kernel.org>
> > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > ---
> > >  drivers/cpuidle/governors/teo.c |    7 ++-----
> > >  1 file changed, 2 insertions(+), 5 deletions(-)
> > >
> > > --- a/drivers/cpuidle/governors/teo.c
> > > +++ b/drivers/cpuidle/governors/teo.c
> > > @@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
> > >        * If the closest expected timer is before the target residency of the
> > >        * candidate state, a shallower one needs to be found.
> > >        */
> > > -     if (drv->states[idx].target_residency_ns > duration_ns) {
> > > -             i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> > > -             if (teo_state_ok(i, drv))
> > > -                     idx = i;
> > > -     }
> > > +     if (drv->states[idx].target_residency_ns > duration_ns)
> > > +             idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> > >
> > >       /*
> > >        * If the selected state's target residency is below the tick length
> > >
> > >
> > >
> >
> > AFAICT this check was to not be stuck in a shallow state when tick is already disabled.
> > There might be a timer armed in t+500us but that might still get cancelled, which
> > is why we didn't think a below TICK_NSEC 'shallow' state is acceptable?
>
> This is all about hrtimers which are not expected to be canceled too
> often and real energy is wasted here by going too deep if the timer is
> not canceled.

Overall, both teo and menu assume that the timers reported by
tick_nohz_get_sleep_length() will trigger.  Otherwise, calling it
would be kind of pointless ...

Re: [PATCH v1 1/4] cpuidle: governors: teo: Drop incorrect target residency check

[Rafael J. Wysocki]

On Thu, Nov 13, 2025 at 12:47 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Nov 13, 2025 at 12:41 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Thu, Nov 13, 2025 at 12:32 PM Christian Loehle
> > <christian.loehle@arm.com> wrote:
> > >
> > > On 11/12/25 16:22, Rafael J. Wysocki wrote:
> > > > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > >
> > > > When the target residency of the current candidate idle state is
> > > > greater than the expected time till the closest timer (the sleep
> > > > length), it does not matter whether or not the tick has already
> > > > been stopped or if it is going to be stopped.  The closest timer
> > > > will trigger anyway at its due time, so it does not make sense to
> > > > select an idle state with target residency above the sleep length.
> > > >
> > > > Accordingly, drop the teo_state_ok() check done in that case and
> > > > let the governor use the teo_find_shallower_state() return value
> > > > as the new candidate idle state index.
> > > >
> > > > Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
> > > > Cc: All applicable <stable@vger.kernel.org>
> > > > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > > > ---
> > > >  drivers/cpuidle/governors/teo.c |    7 ++-----
> > > >  1 file changed, 2 insertions(+), 5 deletions(-)
> > > >
> > > > --- a/drivers/cpuidle/governors/teo.c
> > > > +++ b/drivers/cpuidle/governors/teo.c
> > > > @@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
> > > >        * If the closest expected timer is before the target residency of the
> > > >        * candidate state, a shallower one needs to be found.
> > > >        */
> > > > -     if (drv->states[idx].target_residency_ns > duration_ns) {
> > > > -             i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> > > > -             if (teo_state_ok(i, drv))
> > > > -                     idx = i;
> > > > -     }
> > > > +     if (drv->states[idx].target_residency_ns > duration_ns)
> > > > +             idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> > > >
> > > >       /*
> > > >        * If the selected state's target residency is below the tick length
> > > >
> > > >
> > > >
> > >
> > > AFAICT this check was to not be stuck in a shallow state when tick is already disabled.
> > > There might be a timer armed in t+500us but that might still get cancelled, which
> > > is why we didn't think a below TICK_NSEC 'shallow' state is acceptable?
> >
> > This is all about hrtimers which are not expected to be canceled too
> > often and real energy is wasted here by going too deep if the timer is
> > not canceled.
>
> Overall, both teo and menu assume that the timers reported by
> tick_nohz_get_sleep_length() will trigger.  Otherwise, calling it
> would be kind of pointless ...

Anyway, I've sent a v2 of the $subject patch with a more elaborate changelog:

https://lore.kernel.org/linux-pm/5955081.DvuYhMxLoT@rafael.j.wysocki/

Hopefully, it is more convincing.

[PATCH v2 1/4] cpuidle: governors: teo: Drop misguided target residency check

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

When the target residency of the current candidate idle state is
greater than the expected time till the closest timer (the sleep
length), it does not matter whether or not the tick has already been
stopped or if it is going to be stopped.  The closest timer will
trigger anyway at its due time, so if an idle state with target
residency above the sleep length is selected, energy will be wasted
and there may be excess latency.

Of course, if the closest timer were canceled before it could trigger,
a deeper idle state would be more suitable, but this is not expected
to happen (generally speaking, hrtimers are not expected to be
canceled as a rule).

Accordingly, the teo_state_ok() check done in that case causes energy to
be wasted more often than it allows any energy to be saved (if it allows
any energy to be saved at all), so drop it and let the governor use the
teo_find_shallower_state() return value as the new candidate idle state
index.

Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v1 -> v2: Subject and changelog modifications

---
 drivers/cpuidle/governors/teo.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
 	 * If the closest expected timer is before the target residency of the
 	 * candidate state, a shallower one needs to be found.
 	 */
-	if (drv->states[idx].target_residency_ns > duration_ns) {
-		i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
-		if (teo_state_ok(i, drv))
-			idx = i;
-	}
+	if (drv->states[idx].target_residency_ns > duration_ns)
+		idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
 
 	/*
 	 * If the selected state's target residency is below the tick length

Re: [PATCH v2 1/4] cpuidle: governors: teo: Drop misguided target residency check

[Christian Loehle]

On 11/13/25 13:24, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> When the target residency of the current candidate idle state is
> greater than the expected time till the closest timer (the sleep
> length), it does not matter whether or not the tick has already been
> stopped or if it is going to be stopped.  The closest timer will
> trigger anyway at its due time, so if an idle state with target
> residency above the sleep length is selected, energy will be wasted
> and there may be excess latency.
> 
> Of course, if the closest timer were canceled before it could trigger,
> a deeper idle state would be more suitable, but this is not expected
> to happen (generally speaking, hrtimers are not expected to be
> canceled as a rule).
> 
> Accordingly, the teo_state_ok() check done in that case causes energy to
> be wasted more often than it allows any energy to be saved (if it allows
> any energy to be saved at all), so drop it and let the governor use the
> teo_find_shallower_state() return value as the new candidate idle state
> index.
> 
> Fixes: 21d28cd2fa5f ("cpuidle: teo: Do not call tick_nohz_get_sleep_length() upfront")
> Cc: All applicable <stable@vger.kernel.org>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
> 
> v1 -> v2: Subject and changelog modifications
> 
> ---
>  drivers/cpuidle/governors/teo.c |    7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -458,11 +458,8 @@ static int teo_select(struct cpuidle_dri
>  	 * If the closest expected timer is before the target residency of the
>  	 * candidate state, a shallower one needs to be found.
>  	 */
> -	if (drv->states[idx].target_residency_ns > duration_ns) {
> -		i = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> -		if (teo_state_ok(i, drv))
> -			idx = i;
> -	}
> +	if (drv->states[idx].target_residency_ns > duration_ns)
> +		idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
>  
>  	/*
>  	 * If the selected state's target residency is below the tick length
> 

Reviewed-by: Christian Loehle <christian.loehle@arm.com>

[PATCH v1 2/4] cpuidle: governors: teo: Drop redundant function parameter

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

The last no_poll parameter of teo_find_shallower_state() is always
false, so drop it.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/teo.c |   10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -239,17 +239,15 @@ static bool teo_state_ok(int i, struct c
  * @dev: Target CPU.
  * @state_idx: Index of the capping idle state.
  * @duration_ns: Idle duration value to match.
- * @no_poll: Don't consider polling states.
  */
 static int teo_find_shallower_state(struct cpuidle_driver *drv,
 				    struct cpuidle_device *dev, int state_idx,
-				    s64 duration_ns, bool no_poll)
+				    s64 duration_ns)
 {
 	int i;
 
 	for (i = state_idx - 1; i >= 0; i--) {
-		if (dev->states_usage[i].disable ||
-				(no_poll && drv->states[i].flags & CPUIDLE_FLAG_POLLING))
+		if (dev->states_usage[i].disable)
 			continue;
 
 		state_idx = i;
@@ -459,7 +457,7 @@ static int teo_select(struct cpuidle_dri
 	 * candidate state, a shallower one needs to be found.
 	 */
 	if (drv->states[idx].target_residency_ns > duration_ns)
-		idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
+		idx = teo_find_shallower_state(drv, dev, idx, duration_ns);
 
 	/*
 	 * If the selected state's target residency is below the tick length
@@ -487,7 +485,7 @@ end:
 	 */
 	if (idx > idx0 &&
 	    drv->states[idx].target_residency_ns > delta_tick)
-		idx = teo_find_shallower_state(drv, dev, idx, delta_tick, false);
+		idx = teo_find_shallower_state(drv, dev, idx, delta_tick);
 
 out_tick:
 	*stop_tick = false;

Re: [PATCH v1 2/4] cpuidle: governors: teo: Drop redundant function parameter

[Christian Loehle]

On 11/12/25 16:23, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> The last no_poll parameter of teo_find_shallower_state() is always
> false, so drop it.
> 
> No intentional functional impact.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Reviewed-by: Christian Loehle <christian.loehle@arm.com>

> ---
>  drivers/cpuidle/governors/teo.c |   10 ++++------
>  1 file changed, 4 insertions(+), 6 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -239,17 +239,15 @@ static bool teo_state_ok(int i, struct c
>   * @dev: Target CPU.
>   * @state_idx: Index of the capping idle state.
>   * @duration_ns: Idle duration value to match.
> - * @no_poll: Don't consider polling states.
>   */
>  static int teo_find_shallower_state(struct cpuidle_driver *drv,
>  				    struct cpuidle_device *dev, int state_idx,
> -				    s64 duration_ns, bool no_poll)
> +				    s64 duration_ns)
>  {
>  	int i;
>  
>  	for (i = state_idx - 1; i >= 0; i--) {
> -		if (dev->states_usage[i].disable ||
> -				(no_poll && drv->states[i].flags & CPUIDLE_FLAG_POLLING))
> +		if (dev->states_usage[i].disable)
>  			continue;
>  
>  		state_idx = i;
> @@ -459,7 +457,7 @@ static int teo_select(struct cpuidle_dri
>  	 * candidate state, a shallower one needs to be found.
>  	 */
>  	if (drv->states[idx].target_residency_ns > duration_ns)
> -		idx = teo_find_shallower_state(drv, dev, idx, duration_ns, false);
> +		idx = teo_find_shallower_state(drv, dev, idx, duration_ns);
>  
>  	/*
>  	 * If the selected state's target residency is below the tick length
> @@ -487,7 +485,7 @@ end:
>  	 */
>  	if (idx > idx0 &&
>  	    drv->states[idx].target_residency_ns > delta_tick)
> -		idx = teo_find_shallower_state(drv, dev, idx, delta_tick, false);
> +		idx = teo_find_shallower_state(drv, dev, idx, delta_tick);
>  
>  out_tick:
>  	*stop_tick = false;
> 
> 
> 

[PATCH v1 3/4] cpuidle: governors: teo: Use s64 consistently in teo_update()

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Two local variables in teo_update() are defined as u64, but their
values are then compared with s64 values, so it is more consistent
to use s64 as their data type.

No intentional functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/teo.c |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -157,8 +157,7 @@ static void teo_update(struct cpuidle_dr
 {
 	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
 	int i, idx_timer = 0, idx_duration = 0;
-	s64 target_residency_ns;
-	u64 measured_ns;
+	s64 target_residency_ns, measured_ns;
 
 	cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
 
@@ -167,9 +166,9 @@ static void teo_update(struct cpuidle_dr
 		 * If one of the safety nets has triggered, assume that this
 		 * might have been a long sleep.
 		 */
-		measured_ns = U64_MAX;
+		measured_ns = S64_MAX;
 	} else {
-		u64 lat_ns = drv->states[dev->last_state_idx].exit_latency_ns;
+		s64 lat_ns = drv->states[dev->last_state_idx].exit_latency_ns;
 
 		measured_ns = dev->last_residency_ns;
 		/*

Re: [PATCH v1 3/4] cpuidle: governors: teo: Use s64 consistently in teo_update()

[Christian Loehle]

On 11/12/25 16:24, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> Two local variables in teo_update() are defined as u64, but their
> values are then compared with s64 values, so it is more consistent
> to use s64 as their data type.
> 
> No intentional functional impact.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Reviewed-by: Christian Loehle <christian.loehle@arm.com>

> ---
>  drivers/cpuidle/governors/teo.c |    7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -157,8 +157,7 @@ static void teo_update(struct cpuidle_dr
>  {
>  	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
>  	int i, idx_timer = 0, idx_duration = 0;
> -	s64 target_residency_ns;
> -	u64 measured_ns;
> +	s64 target_residency_ns, measured_ns;
>  
>  	cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
>  
> @@ -167,9 +166,9 @@ static void teo_update(struct cpuidle_dr
>  		 * If one of the safety nets has triggered, assume that this
>  		 * might have been a long sleep.
>  		 */
> -		measured_ns = U64_MAX;
> +		measured_ns = S64_MAX;
>  	} else {
> -		u64 lat_ns = drv->states[dev->last_state_idx].exit_latency_ns;
> +		s64 lat_ns = drv->states[dev->last_state_idx].exit_latency_ns;
>  
>  		measured_ns = dev->last_residency_ns;
>  		/*
> 
> 
> 

[PATCH v1 4/4] cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

If a given governor metric falls below a certain value (8 for
DECAY_SHIFT equal to 3), it will not decay any more due to the
simplistic decay implementation.  This may in some cases lead to
subtle inconsistencies in the governor behavior, so change the
decay implementation to take it into account and set the metric
at hand to 0 in that case.

Suggested-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/teo.c |   20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -148,6 +148,16 @@ struct teo_cpu {
 
 static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
 
+static void teo_decay(unsigned int *metric)
+{
+	unsigned int delta = *metric >> DECAY_SHIFT;
+
+	if (delta)
+		*metric -= delta;
+	else
+		*metric = 0;
+}
+
 /**
  * teo_update - Update CPU metrics after wakeup.
  * @drv: cpuidle driver containing state data.
@@ -159,7 +169,7 @@ static void teo_update(struct cpuidle_dr
 	int i, idx_timer = 0, idx_duration = 0;
 	s64 target_residency_ns, measured_ns;
 
-	cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
+	teo_decay(&cpu_data->short_idles);
 
 	if (cpu_data->artificial_wakeup) {
 		/*
@@ -195,8 +205,8 @@ static void teo_update(struct cpuidle_dr
 	for (i = 0; i < drv->state_count; i++) {
 		struct teo_bin *bin = &cpu_data->state_bins[i];
 
-		bin->hits -= bin->hits >> DECAY_SHIFT;
-		bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
+		teo_decay(&bin->hits);
+		teo_decay(&bin->intercepts);
 
 		target_residency_ns = drv->states[i].target_residency_ns;
 
@@ -207,7 +217,7 @@ static void teo_update(struct cpuidle_dr
 		}
 	}
 
-	cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
+	teo_decay(&cpu_data->tick_intercepts);
 	/*
 	 * If the measured idle duration falls into the same bin as the sleep
 	 * length, this is a "hit", so update the "hits" metric for that bin.
@@ -222,7 +232,7 @@ static void teo_update(struct cpuidle_dr
 			cpu_data->tick_intercepts += PULSE;
 	}
 
-	cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
+	teo_decay(&cpu_data->total);
 	cpu_data->total += PULSE;
 }
 

Re: [PATCH v1 4/4] cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

[Christian Loehle]

On 11/12/25 16:25, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If a given governor metric falls below a certain value (8 for
> DECAY_SHIFT equal to 3), it will not decay any more due to the
> simplistic decay implementation.  This may in some cases lead to
> subtle inconsistencies in the governor behavior, so change the
> decay implementation to take it into account and set the metric
> at hand to 0 in that case.
> 
> Suggested-by: Christian Loehle <christian.loehle@arm.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/cpuidle/governors/teo.c |   20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -148,6 +148,16 @@ struct teo_cpu {
>  
>  static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
>  
> +static void teo_decay(unsigned int *metric)
> +{
> +	unsigned int delta = *metric >> DECAY_SHIFT;
> +
> +	if (delta)
> +		*metric -= delta;
> +	else
> +		*metric = 0;
> +}
> +
>  /**
>   * teo_update - Update CPU metrics after wakeup.
>   * @drv: cpuidle driver containing state data.
> @@ -159,7 +169,7 @@ static void teo_update(struct cpuidle_dr
>  	int i, idx_timer = 0, idx_duration = 0;
>  	s64 target_residency_ns, measured_ns;
>  
> -	cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
> +	teo_decay(&cpu_data->short_idles);
>  
>  	if (cpu_data->artificial_wakeup) {
>  		/*
> @@ -195,8 +205,8 @@ static void teo_update(struct cpuidle_dr
>  	for (i = 0; i < drv->state_count; i++) {
>  		struct teo_bin *bin = &cpu_data->state_bins[i];
>  
> -		bin->hits -= bin->hits >> DECAY_SHIFT;
> -		bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
> +		teo_decay(&bin->hits);
> +		teo_decay(&bin->intercepts);
>  
>  		target_residency_ns = drv->states[i].target_residency_ns;
>  
> @@ -207,7 +217,7 @@ static void teo_update(struct cpuidle_dr
>  		}
>  	}
>  
> -	cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
> +	teo_decay(&cpu_data->tick_intercepts);
>  	/*
>  	 * If the measured idle duration falls into the same bin as the sleep
>  	 * length, this is a "hit", so update the "hits" metric for that bin.
> @@ -222,7 +232,7 @@ static void teo_update(struct cpuidle_dr
>  			cpu_data->tick_intercepts += PULSE;
>  	}
>  
> -	cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
> +	teo_decay(&cpu_data->total);
>  	cpu_data->total += PULSE;

This will result in total no longer being a strict sum of the bins.
Any reason not to do something like:

-----8<-----

diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
index e5b795cf3155..ff58d70ee80d 100644
--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -148,14 +148,19 @@ struct teo_cpu {
 
 static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
 
-static void teo_decay(unsigned int *metric)
+static unsigned int teo_decay(unsigned int *metric)
 {
        unsigned int delta = *metric >> DECAY_SHIFT;
+       unsigned int decay;
 
-       if (delta)
+       if (delta) {
                *metric -= delta;
-       else
-               *metric = 0;
+               return delta;
+       }
+
+       decay = *metric;
+       *metric = 0;
+       return decay;
 }
 
 /**
@@ -168,6 +173,7 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
        struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
        int i, idx_timer = 0, idx_duration = 0;
        s64 target_residency_ns, measured_ns;
+       unsigned int total_decay = 0;
 
        teo_decay(&cpu_data->short_idles);
 
@@ -205,8 +211,8 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
        for (i = 0; i < drv->state_count; i++) {
                struct teo_bin *bin = &cpu_data->state_bins[i];
 
-               teo_decay(&bin->hits);
-               teo_decay(&bin->intercepts);
+               total_decay += teo_decay(&bin->hits);
+               total_decay += teo_decay(&bin->intercepts);
 
                target_residency_ns = drv->states[i].target_residency_ns;
 
@@ -232,7 +238,7 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
                        cpu_data->tick_intercepts += PULSE;
        }
 
-       teo_decay(&cpu_data->total);
+       cpu_data->total -= total_decay;
        cpu_data->total += PULSE;
 }
 

Re: [PATCH v1 4/4] cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

[Rafael J. Wysocki]

On Wed, Nov 12, 2025 at 6:29 PM Christian Loehle
<christian.loehle@arm.com> wrote:
>
> On 11/12/25 16:25, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > If a given governor metric falls below a certain value (8 for
> > DECAY_SHIFT equal to 3), it will not decay any more due to the
> > simplistic decay implementation.  This may in some cases lead to
> > subtle inconsistencies in the governor behavior, so change the
> > decay implementation to take it into account and set the metric
> > at hand to 0 in that case.
> >
> > Suggested-by: Christian Loehle <christian.loehle@arm.com>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> > ---
> >  drivers/cpuidle/governors/teo.c |   20 +++++++++++++++-----
> >  1 file changed, 15 insertions(+), 5 deletions(-)
> >
> > --- a/drivers/cpuidle/governors/teo.c
> > +++ b/drivers/cpuidle/governors/teo.c
> > @@ -148,6 +148,16 @@ struct teo_cpu {
> >
> >  static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
> >
> > +static void teo_decay(unsigned int *metric)
> > +{
> > +     unsigned int delta = *metric >> DECAY_SHIFT;
> > +
> > +     if (delta)
> > +             *metric -= delta;
> > +     else
> > +             *metric = 0;
> > +}
> > +
> >  /**
> >   * teo_update - Update CPU metrics after wakeup.
> >   * @drv: cpuidle driver containing state data.
> > @@ -159,7 +169,7 @@ static void teo_update(struct cpuidle_dr
> >       int i, idx_timer = 0, idx_duration = 0;
> >       s64 target_residency_ns, measured_ns;
> >
> > -     cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
> > +     teo_decay(&cpu_data->short_idles);
> >
> >       if (cpu_data->artificial_wakeup) {
> >               /*
> > @@ -195,8 +205,8 @@ static void teo_update(struct cpuidle_dr
> >       for (i = 0; i < drv->state_count; i++) {
> >               struct teo_bin *bin = &cpu_data->state_bins[i];
> >
> > -             bin->hits -= bin->hits >> DECAY_SHIFT;
> > -             bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
> > +             teo_decay(&bin->hits);
> > +             teo_decay(&bin->intercepts);
> >
> >               target_residency_ns = drv->states[i].target_residency_ns;
> >
> > @@ -207,7 +217,7 @@ static void teo_update(struct cpuidle_dr
> >               }
> >       }
> >
> > -     cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
> > +     teo_decay(&cpu_data->tick_intercepts);
> >       /*
> >        * If the measured idle duration falls into the same bin as the sleep
> >        * length, this is a "hit", so update the "hits" metric for that bin.
> > @@ -222,7 +232,7 @@ static void teo_update(struct cpuidle_dr
> >                       cpu_data->tick_intercepts += PULSE;
> >       }
> >
> > -     cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
> > +     teo_decay(&cpu_data->total);
> >       cpu_data->total += PULSE;
>
> This will result in total no longer being a strict sum of the bins.

Ah, good point.

> Any reason not to do something like:

Well, it would be more straightforward to just compute "total" from
scratch instead of using total_decay (it would be the same amount of
computation minus the teo_decay() changes AFAICS).

I'll send an update of this patch.

Re: [PATCH v1 4/4] cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

[Christian Loehle]

On 11/12/25 17:51, Rafael J. Wysocki wrote:
> On Wed, Nov 12, 2025 at 6:29 PM Christian Loehle
> <christian.loehle@arm.com> wrote:
>>
>> On 11/12/25 16:25, Rafael J. Wysocki wrote:
>>> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>
>>> If a given governor metric falls below a certain value (8 for
>>> DECAY_SHIFT equal to 3), it will not decay any more due to the
>>> simplistic decay implementation.  This may in some cases lead to
>>> subtle inconsistencies in the governor behavior, so change the
>>> decay implementation to take it into account and set the metric
>>> at hand to 0 in that case.
>>>
>>> Suggested-by: Christian Loehle <christian.loehle@arm.com>
>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>> ---
>>>  drivers/cpuidle/governors/teo.c |   20 +++++++++++++++-----
>>>  1 file changed, 15 insertions(+), 5 deletions(-)
>>>
>>> --- a/drivers/cpuidle/governors/teo.c
>>> +++ b/drivers/cpuidle/governors/teo.c
>>> @@ -148,6 +148,16 @@ struct teo_cpu {
>>>
>>>  static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
>>>
>>> +static void teo_decay(unsigned int *metric)
>>> +{
>>> +     unsigned int delta = *metric >> DECAY_SHIFT;
>>> +
>>> +     if (delta)
>>> +             *metric -= delta;
>>> +     else
>>> +             *metric = 0;
>>> +}
>>> +
>>>  /**
>>>   * teo_update - Update CPU metrics after wakeup.
>>>   * @drv: cpuidle driver containing state data.
>>> @@ -159,7 +169,7 @@ static void teo_update(struct cpuidle_dr
>>>       int i, idx_timer = 0, idx_duration = 0;
>>>       s64 target_residency_ns, measured_ns;
>>>
>>> -     cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
>>> +     teo_decay(&cpu_data->short_idles);
>>>
>>>       if (cpu_data->artificial_wakeup) {
>>>               /*
>>> @@ -195,8 +205,8 @@ static void teo_update(struct cpuidle_dr
>>>       for (i = 0; i < drv->state_count; i++) {
>>>               struct teo_bin *bin = &cpu_data->state_bins[i];
>>>
>>> -             bin->hits -= bin->hits >> DECAY_SHIFT;
>>> -             bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
>>> +             teo_decay(&bin->hits);
>>> +             teo_decay(&bin->intercepts);
>>>
>>>               target_residency_ns = drv->states[i].target_residency_ns;
>>>
>>> @@ -207,7 +217,7 @@ static void teo_update(struct cpuidle_dr
>>>               }
>>>       }
>>>
>>> -     cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
>>> +     teo_decay(&cpu_data->tick_intercepts);
>>>       /*
>>>        * If the measured idle duration falls into the same bin as the sleep
>>>        * length, this is a "hit", so update the "hits" metric for that bin.
>>> @@ -222,7 +232,7 @@ static void teo_update(struct cpuidle_dr
>>>                       cpu_data->tick_intercepts += PULSE;
>>>       }
>>>
>>> -     cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
>>> +     teo_decay(&cpu_data->total);
>>>       cpu_data->total += PULSE;
>>
>> This will result in total no longer being a strict sum of the bins.
> 
> Ah, good point.
> 
>> Any reason not to do something like:
> 
> Well, it would be more straightforward to just compute "total" from
> scratch instead of using total_decay (it would be the same amount of
> computation minus the teo_decay() changes AFAICS).

Duh, of course...

> 
> I'll send an update of this patch.

Thanks!

[PATCH v2 4/4] cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

If a given governor metric falls below a certain value (8 for
DECAY_SHIFT equal to 3), it will not decay any more due to the
simplistic decay implementation.  This may in some cases lead to
subtle inconsistencies in the governor behavior, so change the
decay implementation to take it into account and set the metric
at hand to 0 in that case.

Suggested-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v1 -> v2:
   * Ensure that cpu_data->total is always the sum of the intercepts and hits
     metrics for all of the idle states (Christian).

---
 drivers/cpuidle/governors/teo.c |   26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -148,6 +148,16 @@ struct teo_cpu {
 
 static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
 
+static void teo_decay(unsigned int *metric)
+{
+	unsigned int delta = *metric >> DECAY_SHIFT;
+
+	if (delta)
+		*metric -= delta;
+	else
+		*metric = 0;
+}
+
 /**
  * teo_update - Update CPU metrics after wakeup.
  * @drv: cpuidle driver containing state data.
@@ -158,8 +168,9 @@ static void teo_update(struct cpuidle_dr
 	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
 	int i, idx_timer = 0, idx_duration = 0;
 	s64 target_residency_ns, measured_ns;
+	unsigned int total = 0;
 
-	cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
+	teo_decay(&cpu_data->short_idles);
 
 	if (cpu_data->artificial_wakeup) {
 		/*
@@ -195,8 +206,10 @@ static void teo_update(struct cpuidle_dr
 	for (i = 0; i < drv->state_count; i++) {
 		struct teo_bin *bin = &cpu_data->state_bins[i];
 
-		bin->hits -= bin->hits >> DECAY_SHIFT;
-		bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
+		teo_decay(&bin->hits);
+		total += bin->hits;
+		teo_decay(&bin->intercepts);
+		total += bin->intercepts;
 
 		target_residency_ns = drv->states[i].target_residency_ns;
 
@@ -207,7 +220,9 @@ static void teo_update(struct cpuidle_dr
 		}
 	}
 
-	cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
+	cpu_data->total = total + PULSE;
+
+	teo_decay(&cpu_data->tick_intercepts);
 	/*
 	 * If the measured idle duration falls into the same bin as the sleep
 	 * length, this is a "hit", so update the "hits" metric for that bin.
@@ -221,9 +236,6 @@ static void teo_update(struct cpuidle_dr
 		if (TICK_NSEC <= measured_ns)
 			cpu_data->tick_intercepts += PULSE;
 	}
-
-	cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
-	cpu_data->total += PULSE;
 }
 
 static bool teo_state_ok(int i, struct cpuidle_driver *drv)

Re: [PATCH v2 4/4] cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

[Christian Loehle]

On 11/12/25 18:03, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> 
> If a given governor metric falls below a certain value (8 for
> DECAY_SHIFT equal to 3), it will not decay any more due to the
> simplistic decay implementation.  This may in some cases lead to
> subtle inconsistencies in the governor behavior, so change the
> decay implementation to take it into account and set the metric
> at hand to 0 in that case.
> 
> Suggested-by: Christian Loehle <christian.loehle@arm.com>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Reviewed-by: Christian Loehle <christian.loehle@arm.com>

> ---
> 
> v1 -> v2:
>    * Ensure that cpu_data->total is always the sum of the intercepts and hits
>      metrics for all of the idle states (Christian).
> 
> ---
>  drivers/cpuidle/governors/teo.c |   26 +++++++++++++++++++-------
>  1 file changed, 19 insertions(+), 7 deletions(-)
> 
> --- a/drivers/cpuidle/governors/teo.c
> +++ b/drivers/cpuidle/governors/teo.c
> @@ -148,6 +148,16 @@ struct teo_cpu {
>  
>  static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
>  
> +static void teo_decay(unsigned int *metric)
> +{
> +	unsigned int delta = *metric >> DECAY_SHIFT;
> +
> +	if (delta)
> +		*metric -= delta;
> +	else
> +		*metric = 0;
> +}
> +
>  /**
>   * teo_update - Update CPU metrics after wakeup.
>   * @drv: cpuidle driver containing state data.
> @@ -158,8 +168,9 @@ static void teo_update(struct cpuidle_dr
>  	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
>  	int i, idx_timer = 0, idx_duration = 0;
>  	s64 target_residency_ns, measured_ns;
> +	unsigned int total = 0;
>  
> -	cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
> +	teo_decay(&cpu_data->short_idles);
>  
>  	if (cpu_data->artificial_wakeup) {
>  		/*
> @@ -195,8 +206,10 @@ static void teo_update(struct cpuidle_dr
>  	for (i = 0; i < drv->state_count; i++) {
>  		struct teo_bin *bin = &cpu_data->state_bins[i];
>  
> -		bin->hits -= bin->hits >> DECAY_SHIFT;
> -		bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
> +		teo_decay(&bin->hits);
> +		total += bin->hits;
> +		teo_decay(&bin->intercepts);
> +		total += bin->intercepts;
>  
>  		target_residency_ns = drv->states[i].target_residency_ns;
>  
> @@ -207,7 +220,9 @@ static void teo_update(struct cpuidle_dr
>  		}
>  	}
>  
> -	cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
> +	cpu_data->total = total + PULSE;
> +
> +	teo_decay(&cpu_data->tick_intercepts);
>  	/*
>  	 * If the measured idle duration falls into the same bin as the sleep
>  	 * length, this is a "hit", so update the "hits" metric for that bin.
> @@ -221,9 +236,6 @@ static void teo_update(struct cpuidle_dr
>  		if (TICK_NSEC <= measured_ns)
>  			cpu_data->tick_intercepts += PULSE;
>  	}
> -
> -	cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
> -	cpu_data->total += PULSE;
>  }
>  
>  static bool teo_state_ok(int i, struct cpuidle_driver *drv)
> 
> 
> 

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Christian Loehle]

On 11/12/25 16:21, Rafael J. Wysocki wrote:
> Hi,
> 
> This is a bunch of teo cpuidle governor improvements, some of which are related
> to a bug report discussed recently:
> 
> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
> 
> The first patch fixes a bug that may cause an overly deep idle state
> to be selected when the scheduler tick has been already stopped.
> 
> Patch [2/4] removes an unnecessary function argument.
> 
> Patch [3/4] makes teo_update() to use s64 as the data type for its local
> variables more consistently.
> 
> The last patch reworks the governor's decay implementation to also decay
> metric values lower than 8.
> 

Tested-by: Christian Loehle <christian.loehle@arm.com>

Test results below, although there really isn't anything interesting in there.
teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
teo-m = mainline)


device     gov        iter     iops      idles  idle_miss      ratio     belows     aboves
mmcblk1    teo-m      0      2330     644806         69      0.000         47         22
mmcblk1    teo-m      1      2328     642994        102      0.000         66         36
mmcblk1    teo-m      2      2352     644020         44      0.000         28         16
mmcblk1    teo-1      0      2324     582886        174      0.000         52        122
mmcblk1    teo-1      1      2350     584012         57      0.000         45         12
mmcblk1    teo-1      2      2329     642238         55      0.000         36         19
mmcblk1    teo-2      0      2327     627590         90      0.000         40         50
mmcblk1    teo-2      1      2328     640178         62      0.000         43         19
mmcblk1    teo-2      2      2327     590950        109      0.000         97         12
mmcblk1    teo-3      0      2328     644366         55      0.000         41         14
mmcblk1    teo-3      1      2327     642740         57      0.000         31         26
mmcblk1    teo-3      2      2327     638428         77      0.000         51         26
mmcblk1    teo-4      0      2326     614326        137      0.000         35        102
mmcblk1    teo-4      1      2328     639990         29      0.000         24          5
mmcblk1    teo-4      2      2327     643086         62      0.000         41         21
mmcblk1    teo-6-6    0      2329     596768       1753      0.003       1686         67
mmcblk1    teo-6-6    1      2330     600324       1527      0.003       1495         32
mmcblk1    teo-6-6    2      2331     600110       1439      0.002       1397         42
mmcblk1    teo-6-12   0      2347     741170          6      0.000          4          2
mmcblk1    teo-6-12   1      2329     782232          0      0.000          4          2
mmcblk1    teo-6-12   2      2328     775652         10      0.000          8          2
mmcblk2    teo-m      0      5758     860660         61      0.000         47         14
mmcblk2    teo-m      1      5731     827264        493      0.001        477         16
mmcblk2    teo-m      2      5700     861346         69      0.000         50         19
mmcblk2    teo-1      0      5663     848222        708      0.001        666         42
mmcblk2    teo-1      1      5648     704886        563      0.001        528         35
mmcblk2    teo-1      2      5655     705698        208      0.000        161         47
mmcblk2    teo-2      0      5697     908264        326      0.000        316         10
mmcblk2    teo-2      1      5656     720270        592      0.001        515         77
mmcblk2    teo-2      2      5641     673948        540      0.001        501         39
mmcblk2    teo-3      0      5675     724770        709      0.001        666         43
mmcblk2    teo-3      1      5675     792828       1144      0.001        892        252
mmcblk2    teo-3      2      5701     909848        660      0.001        332        328
mmcblk2    teo-4      0      5673     860736        798      0.001        791          7
mmcblk2    teo-4      1      5606     508886       1786      0.004       1727         59
mmcblk2    teo-4      2      5632     569238        104      0.000         73         31
mmcblk2    teo-6-6    0      5692     848824       1748      0.002       1685         63
mmcblk2    teo-6-6    1      5898     876180       1225      0.001       1215         10
mmcblk2    teo-6-6    2      5646     633846       2248      0.004       2199         49
mmcblk2    teo-6-12   0      5869    1009742          9      0.000          6          3
mmcblk2    teo-6-12   1      5644     775326          4      0.000          4          0
mmcblk2    teo-6-12   2      5671     904480          4      0.000          4          0
nvme0n1    teo-m      0     10342     765802        152      0.000         55         97
nvme0n1    teo-m      1     10703     789232        157      0.000         52        105
nvme0n1    teo-m      2     10405     770046         62      0.000         34         28
nvme0n1    teo-1      0     10687     782984         84      0.000         40         44
nvme0n1    teo-1      1     11326     829102         79      0.000         33         46
nvme0n1    teo-1      2     10636     780884        197      0.000         98         99
nvme0n1    teo-2      0     10951     803155        108      0.000         39         69
nvme0n1    teo-2      1     11468     837334         55      0.000         35         20
nvme0n1    teo-2      2     10410     773154        148      0.000         63         85
nvme0n1    teo-3      0     10701     787882        101      0.000         47         54
nvme0n1    teo-3      1     10403     767178         54      0.000         31         23
nvme0n1    teo-3      2     10749     785898        209      0.000         51        158
nvme0n1    teo-4      0     10462     768442        149      0.000         56         93
nvme0n1    teo-4      1     10642     777534         85      0.000         45         40
nvme0n1    teo-4      2     10486     775710        172      0.000         62        110
nvme0n1    teo-6-6    0     11507     798450       1564      0.002       1505         59
nvme0n1    teo-6-6    1     10499     735294       2009      0.003       1879        130
nvme0n1    teo-6-6    2     10598     740936       1756      0.002       1477        279
nvme0n1    teo-6-12   0     10542     922846         18      0.000         12          6
nvme0n1    teo-6-12   1     10482     922114         23      0.000         16          7
nvme0n1    teo-6-12   2     11046     940398         23      0.000         17          6
sda        teo-m      0      1269     778958        111      0.000        108          3
sda        teo-m      1      1268     831064       1064      0.001       1054         10
sda        teo-m      2      1270     803714       2044      0.003       2034         10
sda        teo-1      0      1273     776836        143      0.000        131         12
sda        teo-1      1      1272     801800       2043      0.003       2043          0
sda        teo-1      2      1270     788906        165      0.000        155         10
sda        teo-2      0      1271     763694         79      0.000         68         11
sda        teo-2      1      1270     753904         66      0.000         62          4
sda        teo-2      2      1272     806804         45      0.000         38          7
sda        teo-3      0      1271     812758       1497      0.002       1494          3
sda        teo-3      1      1270     800006         49      0.000         48          1
sda        teo-3      2      1272     829854        358      0.000        356          2
sda        teo-4      0      1270     886646        243      0.000        239          4
sda        teo-4      1      1269     820968         40      0.000         38          2
sda        teo-4      2      1272     835716        124      0.000        109         15
sda        teo-6-6    0      1257     591486       5450      0.009       5435         15
sda        teo-6-6    1      1265     788536       4412      0.006       4404          8
sda        teo-6-6    2      1254     788282       4470      0.006       4461          9
sda        teo-6-12   0      1274     841398          0      0.000       4461          9
sda        teo-6-12   1      1271     840824          0      0.000       4461          9
sda        teo-6-12   2      1272     923816          4      0.000          4          0
nullb0     teo-m      0    101284     114406        178      0.002         70        108
nullb0     teo-m      1    101381     112804        496      0.004        303        193
nullb0     teo-m      2    101716     100370        380      0.004        225        155
nullb0     teo-1      0    101353     101198        366      0.004        202        164
nullb0     teo-1      1    100571     105004        168      0.002         87         81
nullb0     teo-1      2    101311     110644         56      0.001         26         30
nullb0     teo-2      0    100961     113126        261      0.002        159        102
nullb0     teo-2      1    101346     111776        463      0.004        261        202
nullb0     teo-2      2    101287     109772        277      0.003        137        140
nullb0     teo-3      0    101448     113264        239      0.002        141         98
nullb0     teo-3      1    101077     112294        301      0.003         47        254
nullb0     teo-3      2    100097     116756        423      0.004        267        156
nullb0     teo-4      0     99562     109606         52      0.000         30         22
nullb0     teo-4      1    101131     113982        136      0.001         45         91
nullb0     teo-4      2    100618     113698        144      0.001         41        103
nullb0     teo-6-6    0    101295      74346       2369      0.032       2139        230
nullb0     teo-6-6    1    101299      75350       1943      0.026       1803        140
nullb0     teo-6-6    2    100578      73924       2317      0.031       2089        228
nullb0     teo-6-12   0    100005     269180          7      0.000          4          3
nullb0     teo-6-12   1    100705     315302          0      0.000          4          3
nullb0     teo-6-12   2    100861     293350          6      0.000          3          3
mtdblock3  teo-m      0       262     312586         66      0.000         47         19
mtdblock3  teo-m      1       259     635682        100      0.000         97          3
mtdblock3  teo-m      2       258     771110        128      0.000         89         39
mtdblock3  teo-1      0       256     601566       7409      0.012       7396         13
mtdblock3  teo-1      1       260     535040         75      0.000         55         20
mtdblock3  teo-1      2       259     702118       1844      0.003       1820         24
mtdblock3  teo-2      0       261     312978       1813      0.006       1789         24
mtdblock3  teo-2      1       255     891548       3095      0.003       3090          5
mtdblock3  teo-2      2       259     680754        234      0.000        223         11
mtdblock3  teo-3      0       259     649474        102      0.000         94          8
mtdblock3  teo-3      1       260     552324        223      0.000        182         41
mtdblock3  teo-3      2       258     734378       1562      0.002       1551         11
mtdblock3  teo-4      0       257     762430       2438      0.003       2430          8
mtdblock3  teo-4      1       252     894318       9326      0.010       9314         12
mtdblock3  teo-4      2       258     663502       1437      0.002       1421         16
mtdblock3  teo-6-6    0       258     782434       1611      0.002       1572         39
mtdblock3  teo-6-6    1       259     591852       1658      0.003       1532        126
mtdblock3  teo-6-6    2       262     274192       1523      0.006       1432         91
mtdblock3  teo-6-12   0       256     986250         11      0.000         10          1
mtdblock3  teo-6-12   1       258     853982         11      0.000          9          2
mtdblock3  teo-6-12   2       260     654184          7      0.000          6          1

test       gov        i     score  %change    idles  idle_miss  miss_rt   belows   aboves
schbench   teo-m      0       196    0      26276         12      0.000         10          2
schbench   teo-m      1       195   -0      25668         23      0.001         19          4
schbench   teo-m      2       208    6      26180         24      0.001         21          3
schbench   teo-m      3       191   -2      25384          4      0.000          3          1
schbench   teo-m      4       194   -1      26060         31      0.001         21         10
schbench   teo-1      0       195   -0      26476         10      0.000          9          1
schbench   teo-1      1       194   -1      24880          9      0.000          9          0
schbench   teo-1      2       194   -1      24540         10      0.000          8          2
schbench   teo-1      3       195   -1      26246         30      0.001         23          7
schbench   teo-1      4       194   -1      26060         15      0.001         11          4
schbench   teo-2      0       198    1      27150         19      0.001         13          6
schbench   teo-2      1       195   -0      25354          8      0.000          8          0
schbench   teo-2      2       194   -1      24396         21      0.001         18          3
schbench   teo-2      3       193   -1      26044         20      0.001         18          2
schbench   teo-2      4       195   -0      26444         22      0.001         20          2
schbench   teo-3      0       192   -2      24988         10      0.000          9          1
schbench   teo-3      1       193   -1      25936          9      0.000          7          2
schbench   teo-3      2       190   -3      25218         14      0.001         13          1
schbench   teo-3      3       191   -2      25612         12      0.000          9          3
schbench   teo-3      4       192   -2      24892         28      0.001         17         11
schbench   teo-4      0       197    1      26768         16      0.001         14          2
schbench   teo-4      1       193   -1      26352         15      0.001         13          2
schbench   teo-4      2       194   -1      26158         15      0.001         14          1
schbench   teo-4      3       203    4      27536         28      0.001         26          2
schbench   teo-4      4       192   -2      24806         19      0.001         15          4
schbench   teo-6-6    0       199    2      24676        128      0.005        121          7
schbench   teo-6-6    1       211    8      26794        127      0.005        117         10
schbench   teo-6-6    2       205    5      25026        140      0.006        125         15
schbench   teo-6-6    3       198    1      24816        196      0.008        174         22
schbench   teo-6-6    4       198    1      26604        236      0.009        218         18
schbench   teo-6-12   0       190   -3      24464          0      0.000        218         18
schbench   teo-6-12   1       190   -3      25274          0      0.000        218         18
schbench   teo-6-12   2       190   -3      25256          0      0.000        218         18
schbench   teo-6-12   3       199    2      26342          0      0.000        218         18
schbench   teo-6-12   4       188   -4      25508          0      0.000        218         18
ebizzy     teo-m      0     10733    0       1358          7      0.005          7          0
ebizzy     teo-m      1     10750    0       1206         12      0.010          8          4
ebizzy     teo-m      2     10699   -0       1950         24      0.012         23          1
ebizzy     teo-m      3     10773    0       1384         18      0.013         16          2
ebizzy     teo-m      4     10667   -1       2060         24      0.012         23          1
ebizzy     teo-1      0     10770    0       1858         22      0.012         19          3
ebizzy     teo-1      1     10719   -0       1258          4      0.003          4          0
ebizzy     teo-1      2     10704   -0       1422          5      0.004          5          0
ebizzy     teo-1      3     10719   -0       1568         16      0.010         14          2
ebizzy     teo-1      4     10802    1       1288         11      0.009         11          0
ebizzy     teo-2      0     10669   -1       1126         11      0.010          9          2
ebizzy     teo-2      1     10696   -0       1733         18      0.010         14          4
ebizzy     teo-2      2     10676   -1       1620         17      0.010         14          3
ebizzy     teo-2      3     10737    0       1332         10      0.008          9          1
ebizzy     teo-2      4     10696   -0       1290          8      0.006          8          0
ebizzy     teo-3      0     10650   -1       1448         12      0.008          9          3
ebizzy     teo-3      1     10689   -0       1470         12      0.008         12          0
ebizzy     teo-3      2     10642   -1       1612         19      0.012         15          4
ebizzy     teo-3      3     10705   -0       1462         10      0.007          8          2
ebizzy     teo-3      4     10717   -0       1798         21      0.012         19          2
ebizzy     teo-4      0     10625   -1       1324         12      0.009          8          4
ebizzy     teo-4      1     10705   -0       1430         12      0.008         11          1
ebizzy     teo-4      2     10671   -1       1818         19      0.010         16          3
ebizzy     teo-4      3     10688   -0       1616          8      0.005          8          0
ebizzy     teo-4      4     10724   -0       1882         11      0.006          9          2
ebizzy     teo-6-6    0     10659   -1       1442         58      0.040         46         12
ebizzy     teo-6-6    1     10653   -1       1144         43      0.038         41          2
ebizzy     teo-6-6    2     10696   -0       1256         37      0.029         35          2
ebizzy     teo-6-6    3     10710   -0       1168         43      0.037         38          5
ebizzy     teo-6-6    4     10696   -0       1166         47      0.040         43          4
ebizzy     teo-6-12   0     10709   -0       2186          0      0.000         43          4
ebizzy     teo-6-12   1     10687   -0       1688          0      0.000         43          4
ebizzy     teo-6-12   2     10689   -0       2806          0      0.000         43          4
ebizzy     teo-6-12   3     10734    0       1426          0      0.000         43          4
ebizzy     teo-6-12   4     10757    0       2346          0      0.000         43          4
adrestia   teo-m      0         8    0     103680         21      0.000         19          2
adrestia   teo-m      1        12   50     104026         31      0.000         16         15
adrestia   teo-m      2        12   50     104063         32      0.000         24          8
adrestia   teo-m      3        12   50     104768         44      0.000         22         22
adrestia   teo-m      4        12   50     104388         18      0.000         16          2
adrestia   teo-1      0        12   50     104152         26      0.000         15         11
adrestia   teo-1      1        12   50     103556         12      0.000          9          3
adrestia   teo-1      2        11   38     104202         36      0.000         24         12
adrestia   teo-1      3        12   50     104014         25      0.000         17          8
adrestia   teo-1      4        11   38     103388         12      0.000         11          1
adrestia   teo-2      0        12   50     103492         25      0.000         12         13
adrestia   teo-2      1        12   50     103924         29      0.000         17         12
adrestia   teo-2      2        12   50     103674         19      0.000         13          6
adrestia   teo-2      3        12   50     104464         41      0.000         28         13
adrestia   teo-2      4        12   50     103758         16      0.000          8          8
adrestia   teo-3      0        12   50     103984         25      0.000         12         13
adrestia   teo-3      1        11   38     103556         23      0.000         14          9
adrestia   teo-3      2        12   50     104088         22      0.000         17          5
adrestia   teo-3      3        12   50     104430         48      0.000         26         22
adrestia   teo-3      4        12   50     103968         26      0.000         18          8
adrestia   teo-4      0        12   50     103924         19      0.000         14          5
adrestia   teo-4      1         8    0     103228         14      0.000         10          4
adrestia   teo-4      2        12   50     104124         15      0.000         10          5
adrestia   teo-4      3        12   50     104472         22      0.000         16          6
adrestia   teo-4      4        12   50     103554         30      0.000         16         14
adrestia   teo-6-6    0        12   50     102832         61      0.001         51         10
adrestia   teo-6-6    1        12   50     103136         52      0.001         38         14
adrestia   teo-6-6    2        12   50     102882         37      0.000         29          8
adrestia   teo-6-6    3        12   50     103102         51      0.000         40         11
adrestia   teo-6-6    4        12   50     103260         60      0.001         43         17
adrestia   teo-6-12   0        12   50     112320          0      0.000         43         17
adrestia   teo-6-12   1        12   50     114412          0      0.000         43         17
adrestia   teo-6-12   2        11   38     112220          0      0.000         43         17
adrestia   teo-6-12   3        12   50     112028          0      0.000         43         17
adrestia   teo-6-12   4        12   50     112750          0      0.000         43         17

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Rafael J. Wysocki]

On Thu, Nov 13, 2025 at 4:21 PM Christian Loehle
<christian.loehle@arm.com> wrote:
>
> On 11/12/25 16:21, Rafael J. Wysocki wrote:
> > Hi,
> >
> > This is a bunch of teo cpuidle governor improvements, some of which are related
> > to a bug report discussed recently:
> >
> > https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
> >
> > The first patch fixes a bug that may cause an overly deep idle state
> > to be selected when the scheduler tick has been already stopped.
> >
> > Patch [2/4] removes an unnecessary function argument.
> >
> > Patch [3/4] makes teo_update() to use s64 as the data type for its local
> > variables more consistently.
> >
> > The last patch reworks the governor's decay implementation to also decay
> > metric values lower than 8.
> >
>
> Tested-by: Christian Loehle <christian.loehle@arm.com>

Thank you!

> Test results below, although there really isn't anything interesting in there.
> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
> teo-m = mainline)

Good, that's how it should be.

RE: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Doug Smythies]

On 2025.11.13 07:22 Christian Loehle wrote:
> On 11/12/25 16:21, Rafael J. Wysocki wrote:
>> Hi,
>> 
>> This is a bunch of teo cpuidle governor improvements, some of which are related
>> to a bug report discussed recently:
>> 
>> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
>> 
>> The first patch fixes a bug that may cause an overly deep idle state
>> to be selected when the scheduler tick has been already stopped.
>> 
>> Patch [2/4] removes an unnecessary function argument.
>> 
>> Patch [3/4] makes teo_update() to use s64 as the data type for its local
>> variables more consistently.
>> 
>> The last patch reworks the governor's decay implementation to also decay
>> metric values lower than 8.
>> 
>
> Tested-by: Christian Loehle <christian.loehle@arm.com>
>
> Test results below, although there really isn't anything interesting in there.
> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
> teo-m = mainline)

I tested the 4 patch set also, and also found no differences in results above
repeatability noise levels.

Additionally, I added another patch (patch 5 of 4):
"cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
Similar findings.

Additionally, I added another patch (patch 6 of 4):
"sched/idle: disable tick in idle=poll idle entry" [2]
And found only one significant improvement, for only one test,
but only for the TEO idle governor:

Kernel 6.18-rc4:
For a 6 pair fast ping-pong test (meaning no work per token stop):
teo: 5.53 uSec per loop, reference test
4 of 4 patches: 5.53 uSec per loop, 0% 
5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
6 of 4 patches: 4.77 uSec per loop, 13% better
6 of 4 patches (again): 4.81 uSec per loop, 13% better
menu: 5.29 uSec per loop, 4.4% better
menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better

Idle state 0 usage:
18% with patch 6, teo
11% with menu
~1% with mainline and not patch 6, teo.

Idle state 1 usage:
almost 0 with patch 6, teo
~6% with menu
27% with mainline and not patch 6, teo.

Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.

Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.

For clarity my branch log:
3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4

[1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
[2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Rafael J. Wysocki]

On Wed, Nov 19, 2025 at 11:52 PM Doug Smythies <dsmythies@telus.net> wrote:
>
> On 2025.11.13 07:22 Christian Loehle wrote:
> > On 11/12/25 16:21, Rafael J. Wysocki wrote:
> >> Hi,
> >>
> >> This is a bunch of teo cpuidle governor improvements, some of which are related
> >> to a bug report discussed recently:
> >>
> >> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
> >>
> >> The first patch fixes a bug that may cause an overly deep idle state
> >> to be selected when the scheduler tick has been already stopped.
> >>
> >> Patch [2/4] removes an unnecessary function argument.
> >>
> >> Patch [3/4] makes teo_update() to use s64 as the data type for its local
> >> variables more consistently.
> >>
> >> The last patch reworks the governor's decay implementation to also decay
> >> metric values lower than 8.
> >>
> >
> > Tested-by: Christian Loehle <christian.loehle@arm.com>
> >
> > Test results below, although there really isn't anything interesting in there.
> > teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
> > teo-m = mainline)
>
> I tested the 4 patch set also, and also found no differences in results above
> repeatability noise levels.
>
> Additionally, I added another patch (patch 5 of 4):
> "cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
> Similar findings.
>
> Additionally, I added another patch (patch 6 of 4):
> "sched/idle: disable tick in idle=poll idle entry" [2]
> And found only one significant improvement, for only one test,
> but only for the TEO idle governor:
>
> Kernel 6.18-rc4:
> For a 6 pair fast ping-pong test (meaning no work per token stop):
> teo: 5.53 uSec per loop, reference test
> 4 of 4 patches: 5.53 uSec per loop, 0%
> 5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
> 6 of 4 patches: 4.77 uSec per loop, 13% better
> 6 of 4 patches (again): 4.81 uSec per loop, 13% better
> menu: 5.29 uSec per loop, 4.4% better
> menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better
>
> Idle state 0 usage:
> 18% with patch 6, teo
> 11% with menu
> ~1% with mainline and not patch 6, teo.
>
> Idle state 1 usage:
> almost 0 with patch 6, teo
> ~6% with menu
> 27% with mainline and not patch 6, teo.
>
> Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.
>
> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
>
> For clarity my branch log:
> 3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
> d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
> e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
> 7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
> 490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
> 8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
> 6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4
>
> [1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
> [2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/

Thanks for the feedback, much appreciated!

I will likely have some more teo updates in the next cycle.

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Christian Loehle]

On 11/20/25 11:02, Rafael J. Wysocki wrote:
> On Wed, Nov 19, 2025 at 11:52 PM Doug Smythies <dsmythies@telus.net> wrote:
>>
>> On 2025.11.13 07:22 Christian Loehle wrote:
>>> On 11/12/25 16:21, Rafael J. Wysocki wrote:
>>>> Hi,
>>>>
>>>> This is a bunch of teo cpuidle governor improvements, some of which are related
>>>> to a bug report discussed recently:
>>>>
>>>> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
>>>>
>>>> The first patch fixes a bug that may cause an overly deep idle state
>>>> to be selected when the scheduler tick has been already stopped.
>>>>
>>>> Patch [2/4] removes an unnecessary function argument.
>>>>
>>>> Patch [3/4] makes teo_update() to use s64 as the data type for its local
>>>> variables more consistently.
>>>>
>>>> The last patch reworks the governor's decay implementation to also decay
>>>> metric values lower than 8.
>>>>
>>>
>>> Tested-by: Christian Loehle <christian.loehle@arm.com>
>>>
>>> Test results below, although there really isn't anything interesting in there.
>>> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
>>> teo-m = mainline)
>>
>> I tested the 4 patch set also, and also found no differences in results above
>> repeatability noise levels.
>>
>> Additionally, I added another patch (patch 5 of 4):
>> "cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
>> Similar findings.
>>
>> Additionally, I added another patch (patch 6 of 4):
>> "sched/idle: disable tick in idle=poll idle entry" [2]
>> And found only one significant improvement, for only one test,
>> but only for the TEO idle governor:
>>
>> Kernel 6.18-rc4:
>> For a 6 pair fast ping-pong test (meaning no work per token stop):
>> teo: 5.53 uSec per loop, reference test
>> 4 of 4 patches: 5.53 uSec per loop, 0%
>> 5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
>> 6 of 4 patches: 4.77 uSec per loop, 13% better
>> 6 of 4 patches (again): 4.81 uSec per loop, 13% better
>> menu: 5.29 uSec per loop, 4.4% better
>> menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better
>>
>> Idle state 0 usage:
>> 18% with patch 6, teo
>> 11% with menu
>> ~1% with mainline and not patch 6, teo.
>>
>> Idle state 1 usage:
>> almost 0 with patch 6, teo
>> ~6% with menu
>> 27% with mainline and not patch 6, teo.
>>
>> Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.
>>
>> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
>>
>> For clarity my branch log:
>> 3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
>> d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
>> e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
>> 7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
>> 490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
>> 8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
>> 6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4
>>
>> [1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
>> [2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/
> 
> Thanks for the feedback, much appreciated!
> 
> I will likely have some more teo updates in the next cycle.

You're welcome, looking forward to reviewing them too.
I haven't tried to see what this would ideally look like for the -stable branches.
Just backport everything until the most recent applicable Fixes:?

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Rafael J. Wysocki]

On Thu, Nov 20, 2025 at 2:35 PM Christian Loehle
<christian.loehle@arm.com> wrote:
>
> On 11/20/25 11:02, Rafael J. Wysocki wrote:
> > On Wed, Nov 19, 2025 at 11:52 PM Doug Smythies <dsmythies@telus.net> wrote:
> >>
> >> On 2025.11.13 07:22 Christian Loehle wrote:
> >>> On 11/12/25 16:21, Rafael J. Wysocki wrote:
> >>>> Hi,
> >>>>
> >>>> This is a bunch of teo cpuidle governor improvements, some of which are related
> >>>> to a bug report discussed recently:
> >>>>
> >>>> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
> >>>>
> >>>> The first patch fixes a bug that may cause an overly deep idle state
> >>>> to be selected when the scheduler tick has been already stopped.
> >>>>
> >>>> Patch [2/4] removes an unnecessary function argument.
> >>>>
> >>>> Patch [3/4] makes teo_update() to use s64 as the data type for its local
> >>>> variables more consistently.
> >>>>
> >>>> The last patch reworks the governor's decay implementation to also decay
> >>>> metric values lower than 8.
> >>>>
> >>>
> >>> Tested-by: Christian Loehle <christian.loehle@arm.com>
> >>>
> >>> Test results below, although there really isn't anything interesting in there.
> >>> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
> >>> teo-m = mainline)
> >>
> >> I tested the 4 patch set also, and also found no differences in results above
> >> repeatability noise levels.
> >>
> >> Additionally, I added another patch (patch 5 of 4):
> >> "cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
> >> Similar findings.
> >>
> >> Additionally, I added another patch (patch 6 of 4):
> >> "sched/idle: disable tick in idle=poll idle entry" [2]
> >> And found only one significant improvement, for only one test,
> >> but only for the TEO idle governor:
> >>
> >> Kernel 6.18-rc4:
> >> For a 6 pair fast ping-pong test (meaning no work per token stop):
> >> teo: 5.53 uSec per loop, reference test
> >> 4 of 4 patches: 5.53 uSec per loop, 0%
> >> 5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
> >> 6 of 4 patches: 4.77 uSec per loop, 13% better
> >> 6 of 4 patches (again): 4.81 uSec per loop, 13% better
> >> menu: 5.29 uSec per loop, 4.4% better
> >> menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better
> >>
> >> Idle state 0 usage:
> >> 18% with patch 6, teo
> >> 11% with menu
> >> ~1% with mainline and not patch 6, teo.
> >>
> >> Idle state 1 usage:
> >> almost 0 with patch 6, teo
> >> ~6% with menu
> >> 27% with mainline and not patch 6, teo.
> >>
> >> Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.
> >>
> >> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
> >>
> >> For clarity my branch log:
> >> 3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
> >> d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
> >> e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
> >> 7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
> >> 490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
> >> 8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
> >> 6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4
> >>
> >> [1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
> >> [2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/
> >
> > Thanks for the feedback, much appreciated!
> >
> > I will likely have some more teo updates in the next cycle.
>
> You're welcome, looking forward to reviewing them too.
> I haven't tried to see what this would ideally look like for the -stable branches.
> Just backport everything until the most recent applicable Fixes:?

I've added a list to this commit:

https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=14c66155c4609f1a1207d4e716c5e722b8bf920e

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Rafael J. Wysocki]

On Thu, Nov 20, 2025 at 2:38 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Nov 20, 2025 at 2:35 PM Christian Loehle
> <christian.loehle@arm.com> wrote:
> >
> > On 11/20/25 11:02, Rafael J. Wysocki wrote:
> > > On Wed, Nov 19, 2025 at 11:52 PM Doug Smythies <dsmythies@telus.net> wrote:
> > >>
> > >> On 2025.11.13 07:22 Christian Loehle wrote:
> > >>> On 11/12/25 16:21, Rafael J. Wysocki wrote:
> > >>>> Hi,
> > >>>>
> > >>>> This is a bunch of teo cpuidle governor improvements, some of which are related
> > >>>> to a bug report discussed recently:
> > >>>>
> > >>>> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
> > >>>>
> > >>>> The first patch fixes a bug that may cause an overly deep idle state
> > >>>> to be selected when the scheduler tick has been already stopped.
> > >>>>
> > >>>> Patch [2/4] removes an unnecessary function argument.
> > >>>>
> > >>>> Patch [3/4] makes teo_update() to use s64 as the data type for its local
> > >>>> variables more consistently.
> > >>>>
> > >>>> The last patch reworks the governor's decay implementation to also decay
> > >>>> metric values lower than 8.
> > >>>>
> > >>>
> > >>> Tested-by: Christian Loehle <christian.loehle@arm.com>
> > >>>
> > >>> Test results below, although there really isn't anything interesting in there.
> > >>> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
> > >>> teo-m = mainline)
> > >>
> > >> I tested the 4 patch set also, and also found no differences in results above
> > >> repeatability noise levels.
> > >>
> > >> Additionally, I added another patch (patch 5 of 4):
> > >> "cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
> > >> Similar findings.
> > >>
> > >> Additionally, I added another patch (patch 6 of 4):
> > >> "sched/idle: disable tick in idle=poll idle entry" [2]
> > >> And found only one significant improvement, for only one test,
> > >> but only for the TEO idle governor:
> > >>
> > >> Kernel 6.18-rc4:
> > >> For a 6 pair fast ping-pong test (meaning no work per token stop):
> > >> teo: 5.53 uSec per loop, reference test
> > >> 4 of 4 patches: 5.53 uSec per loop, 0%
> > >> 5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
> > >> 6 of 4 patches: 4.77 uSec per loop, 13% better
> > >> 6 of 4 patches (again): 4.81 uSec per loop, 13% better
> > >> menu: 5.29 uSec per loop, 4.4% better
> > >> menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better
> > >>
> > >> Idle state 0 usage:
> > >> 18% with patch 6, teo
> > >> 11% with menu
> > >> ~1% with mainline and not patch 6, teo.
> > >>
> > >> Idle state 1 usage:
> > >> almost 0 with patch 6, teo
> > >> ~6% with menu
> > >> 27% with mainline and not patch 6, teo.
> > >>
> > >> Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.
> > >>
> > >> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
> > >>
> > >> For clarity my branch log:
> > >> 3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
> > >> d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
> > >> e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
> > >> 7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
> > >> 490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
> > >> 8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
> > >> 6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4
> > >>
> > >> [1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
> > >> [2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/
> > >
> > > Thanks for the feedback, much appreciated!
> > >
> > > I will likely have some more teo updates in the next cycle.
> >
> > You're welcome, looking forward to reviewing them too.
> > I haven't tried to see what this would ideally look like for the -stable branches.
> > Just backport everything until the most recent applicable Fixes:?
>
> I've added a list to this commit:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=14c66155c4609f1a1207d4e716c5e722b8bf920e

Which somehow got incorrect git commit hashes, so I need to regenerate
it.  Sorry for the confusion.

Re: [PATCH v1 0/4] cpuidle: governors: teo: Assorted improvements

[Rafael J. Wysocki]

On Thu, Nov 20, 2025 at 2:57 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Thu, Nov 20, 2025 at 2:38 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Thu, Nov 20, 2025 at 2:35 PM Christian Loehle
> > <christian.loehle@arm.com> wrote:
> > >
> > > On 11/20/25 11:02, Rafael J. Wysocki wrote:
> > > > On Wed, Nov 19, 2025 at 11:52 PM Doug Smythies <dsmythies@telus.net> wrote:
> > > >>
> > > >> On 2025.11.13 07:22 Christian Loehle wrote:
> > > >>> On 11/12/25 16:21, Rafael J. Wysocki wrote:
> > > >>>> Hi,
> > > >>>>
> > > >>>> This is a bunch of teo cpuidle governor improvements, some of which are related
> > > >>>> to a bug report discussed recently:
> > > >>>>
> > > >>>> https://lore.kernel.org/linux-pm/CAEmPcwsNMNnNXuxgvHTQ93Mx-q3Oz9U57THQsU_qdcCx1m4w5g@mail.gmail.com/
> > > >>>>
> > > >>>> The first patch fixes a bug that may cause an overly deep idle state
> > > >>>> to be selected when the scheduler tick has been already stopped.
> > > >>>>
> > > >>>> Patch [2/4] removes an unnecessary function argument.
> > > >>>>
> > > >>>> Patch [3/4] makes teo_update() to use s64 as the data type for its local
> > > >>>> variables more consistently.
> > > >>>>
> > > >>>> The last patch reworks the governor's decay implementation to also decay
> > > >>>> metric values lower than 8.
> > > >>>>
> > > >>>
> > > >>> Tested-by: Christian Loehle <christian.loehle@arm.com>
> > > >>>
> > > >>> Test results below, although there really isn't anything interesting in there.
> > > >>> teo-1 to teo-4 (patches 1 to 4 respectively are essentially indistinguishable from
> > > >>> teo-m = mainline)
> > > >>
> > > >> I tested the 4 patch set also, and also found no differences in results above
> > > >> repeatability noise levels.
> > > >>
> > > >> Additionally, I added another patch (patch 5 of 4):
> > > >> "cpuidle: governors: teo: Rework the handling of tick wakeups" [1]
> > > >> Similar findings.
> > > >>
> > > >> Additionally, I added another patch (patch 6 of 4):
> > > >> "sched/idle: disable tick in idle=poll idle entry" [2]
> > > >> And found only one significant improvement, for only one test,
> > > >> but only for the TEO idle governor:
> > > >>
> > > >> Kernel 6.18-rc4:
> > > >> For a 6 pair fast ping-pong test (meaning no work per token stop):
> > > >> teo: 5.53 uSec per loop, reference test
> > > >> 4 of 4 patches: 5.53 uSec per loop, 0%
> > > >> 5 of 4 patches: 5.54 uSec per loop, 0.2% (noise)
> > > >> 6 of 4 patches: 4.77 uSec per loop, 13% better
> > > >> 6 of 4 patches (again): 4.81 uSec per loop, 13% better
> > > >> menu: 5.29 uSec per loop, 4.4% better
> > > >> menu + patch 6 of 4: 5.28 uSec per loop, 4.5% better
> > > >>
> > > >> Idle state 0 usage:
> > > >> 18% with patch 6, teo
> > > >> 11% with menu
> > > >> ~1% with mainline and not patch 6, teo.
> > > >>
> > > >> Idle state 1 usage:
> > > >> almost 0 with patch 6, teo
> > > >> ~6% with menu
> > > >> 27% with mainline and not patch 6, teo.
> > > >>
> > > >> Power: About 100 watts. Patch 6 and teo does increase power use by about a watt or 2.
> > > >>
> > > >> Processor: Intel(R) Core(TM) i5-10600K CPU @ 4.10GHz, 6 cores 12 CPUs.
> > > >>
> > > >> For clarity my branch log:
> > > >> 3993913d7f81 (HEAD -> rjw-teo) sched/idle: disable tick in idle=poll idle entry
> > > >> d9b12b8d62bf cpuidle: governors: teo: Rework the handling of tick wakeups
> > > >> e47178c87272 cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold
> > > >> 7fe32e411c2b cpuidle: governors: teo: Use s64 consistently in teo_update()
> > > >> 490e6118e45d cpuidle: governors: teo: Drop redundant function parameter
> > > >> 8f627f86062e cpuidle: governors: teo: Drop incorrect target residency check
> > > >> 6146a0f1dfae (tag: v6.18-rc4, origin/master, origin/HEAD, master) Linux 6.18-rc4
> > > >>
> > > >> [1] https://lore.kernel.org/linux-pm/6228387.lOV4Wx5bFT@rafael.j.wysocki/
> > > >> [2] https://lore.kernel.org/linux-pm/aQiWfnnSzxsnwa2o@tpad/
> > > >
> > > > Thanks for the feedback, much appreciated!
> > > >
> > > > I will likely have some more teo updates in the next cycle.
> > >
> > > You're welcome, looking forward to reviewing them too.
> > > I haven't tried to see what this would ideally look like for the -stable branches.
> > > Just backport everything until the most recent applicable Fixes:?
> >
> > I've added a list to this commit:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=14c66155c4609f1a1207d4e716c5e722b8bf920e
>
> Which somehow got incorrect git commit hashes, so I need to regenerate
> it.  Sorry for the confusion.

Done, and it's this commit now:

https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=083654ded547238c70e0d4f57115cd1c91245b6e