[RFC] cpuidle - remove the power_specified field in the driver

This patch follows the discussion about reinitializing the power usage
when a C-state is added/removed.

 https://lkml.org/lkml/2012/10/16/518

We realized the power usage field is never filled and when it is
filled for tegra, the power_specified flag is not set making all these
values to be resetted when the driver is initialized with the set_power_state
function.

Julius and I feel this is over-engineered and the power_specified
flag could be simply removed and continue assuming the states are
backward sorted.

The menu governor select function is simplified as the power is ordered.
Actually the condition is always true with the current code.

The cpuidle_play_dead function is also simplified by doing a reverse lookup
on the array.

The set_power_states function is removed as it does no make sense anymore.

Signed-off-by: Daniel Lezcano <redacted>
---
 drivers/cpuidle/cpuidle.c        |   17 ++++-------------
 drivers/cpuidle/driver.c         |   25 -------------------------
 drivers/cpuidle/governors/menu.c |    8 ++------
 include/linux/cpuidle.h          |    2 +-
 4 files changed, 7 insertions(+), 45 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 711dd83..f983262 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c

@@ -69,24 +69,15 @@ int cpuidle_play_dead(void)
 {
 	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
 	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
-	int i, dead_state = -1;
-	int power_usage = -1;
+	int i;
 
 	if (!drv)
 		return -ENODEV;
 
 	/* Find lowest-power state that supports long-term idle */
-	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
-		struct cpuidle_state *s = &drv->states[i];
-
-		if (s->power_usage < power_usage && s->enter_dead) {
-			power_usage = s->power_usage;
-			dead_state = i;
-		}
-	}
-
-	if (dead_state != -1)
-		return drv->states[dead_state].enter_dead(dev, dead_state);
+	for (i = drv->state_count; i >= CPUIDLE_DRIVER_STATE_START; i--)
+		if (drv->states[i].play_dead)
+			return drv->states[i].enter_dead(dev, i);
 
 	return -ENODEV;
 }

diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index 3af841f..bb045f1 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c

@@ -19,34 +19,9 @@ DEFINE_SPINLOCK(cpuidle_driver_lock);
 static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu);
 static struct cpuidle_driver * __cpuidle_get_cpu_driver(int cpu);
 
-static void set_power_states(struct cpuidle_driver *drv)
-{
-	int i;
-
-	/*
-	 * cpuidle driver should set the drv->power_specified bit
-	 * before registering if the driver provides
-	 * power_usage numbers.
-	 *
-	 * If power_specified is not set,
-	 * we fill in power_usage with decreasing values as the
-	 * cpuidle code has an implicit assumption that state Cn
-	 * uses less power than C(n-1).
-	 *
-	 * With CONFIG_ARCH_HAS_CPU_RELAX, C0 is already assigned
-	 * an power value of -1.  So we use -2, -3, etc, for other
-	 * c-states.
-	 */
-	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++)
-		drv->states[i].power_usage = -1 - i;
-}
-
 static void __cpuidle_driver_init(struct cpuidle_driver *drv)
 {
 	drv->refcnt = 0;
-
-	if (!drv->power_specified)
-		set_power_states(drv);
 }
 
 static int __cpuidle_register_driver(struct cpuidle_driver *drv, int cpu)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 2efee27..14eb11f 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c

@@ -312,7 +312,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct menu_device *data = &__get_cpu_var(menu_devices);
 	int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
-	int power_usage = -1;
 	int i;
 	int multiplier;
 	struct timespec t;

@@ -383,11 +382,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 		if (s->exit_latency * multiplier > data->predicted_us)
 			continue;
 
-		if (s->power_usage < power_usage) {
-			power_usage = s->power_usage;
-			data->last_state_idx = i;
-			data->exit_us = s->exit_latency;
-		}
+		data->last_state_idx = i;
+		data->exit_us = s->exit_latency;
 	}
 
 	/* not deepest C-state chosen for low predicted residency */

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 3711b34..24cd103 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h

@@ -126,9 +126,9 @@ struct cpuidle_driver {
 	struct module 		*owner;
 	int                     refcnt;
 
-	unsigned int		power_specified:1;
 	/* set to 1 to use the core cpuidle time keeping (for all states). */
 	unsigned int		en_core_tk_irqen:1;
+	/* states array must be ordered in decreasing power consumption */
 	struct cpuidle_state	states[CPUIDLE_STATE_MAX];
 	int			state_count;
 	int			safe_state_index;

-- 
1.7.5.4

Thanks for moving this along, Daniel. I think this is the right
approach... the cpuidle driver shouldn't be more complex than
necessary.

Note that you are starting your loop too high in cpuidle_play_dead...
states[state_count] is not an actual state anymore, it should start at
state_count - 1. Also, I think you can go ahead and do the same
last-to-first loop transformation with immediate return in the menu
governor, for an extra tiny bit of performance.

On Mon, Nov 12, 2012 at 12:26 PM, Daniel Lezcano
[off-list ref] wrote:

On 11/12/2012 10:09 PM, Julius Werner wrote:

Thanks for moving this along, Daniel. I think this is the right
approach... the cpuidle driver shouldn't be more complex than
necessary.

Note that you are starting your loop too high in cpuidle_play_dead...
states[state_count] is not an actual state anymore, it should start at
state_count - 1. 

Yep. Thanks for catching this.

Also, I think you can go ahead and do the same
last-to-first loop transformation with immediate return in the menu
governor, for an extra tiny bit of performance.

Yes, that makes sense.

Thanks for the review.

  -- Daniel

On Mon, Nov 12, 2012 at 12:26 PM, Daniel Lezcano
[off-list ref] wrote:

quoted

This patch follows the discussion about reinitializing the power usage
when a C-state is added/removed.

 https://lkml.org/lkml/2012/10/16/518

We realized the power usage field is never filled and when it is
filled for tegra, the power_specified flag is not set making all these
values to be resetted when the driver is initialized with the set_power_state
function.

Julius and I feel this is over-engineered and the power_specified
flag could be simply removed and continue assuming the states are
backward sorted.

The menu governor select function is simplified as the power is ordered.
Actually the condition is always true with the current code.

The cpuidle_play_dead function is also simplified by doing a reverse lookup
on the array.

The set_power_states function is removed as it does no make sense anymore.

Signed-off-by: Daniel Lezcano <redacted>
---
 drivers/cpuidle/cpuidle.c        |   17 ++++-------------
 drivers/cpuidle/driver.c         |   25 -------------------------
 drivers/cpuidle/governors/menu.c |    8 ++------
 include/linux/cpuidle.h          |    2 +-
 4 files changed, 7 insertions(+), 45 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 711dd83..f983262 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c

@@ -69,24 +69,15 @@ int cpuidle_play_dead(void)
 {
        struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
        struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
-       int i, dead_state = -1;
-       int power_usage = -1;
+       int i;

        if (!drv)
                return -ENODEV;

        /* Find lowest-power state that supports long-term idle */
-       for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
-               struct cpuidle_state *s = &drv->states[i];
-
-               if (s->power_usage < power_usage && s->enter_dead) {
-                       power_usage = s->power_usage;
-                       dead_state = i;
-               }
-       }
-
-       if (dead_state != -1)
-               return drv->states[dead_state].enter_dead(dev, dead_state);
+       for (i = drv->state_count; i >= CPUIDLE_DRIVER_STATE_START; i--)
+               if (drv->states[i].play_dead)
+                       return drv->states[i].enter_dead(dev, i);

        return -ENODEV;
 }

diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index 3af841f..bb045f1 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c

@@ -19,34 +19,9 @@ DEFINE_SPINLOCK(cpuidle_driver_lock);
 static void __cpuidle_set_cpu_driver(struct cpuidle_driver *drv, int cpu);
 static struct cpuidle_driver * __cpuidle_get_cpu_driver(int cpu);

-static void set_power_states(struct cpuidle_driver *drv)
-{
-       int i;
-
-       /*
-        * cpuidle driver should set the drv->power_specified bit
-        * before registering if the driver provides
-        * power_usage numbers.
-        *
-        * If power_specified is not set,
-        * we fill in power_usage with decreasing values as the
-        * cpuidle code has an implicit assumption that state Cn
-        * uses less power than C(n-1).
-        *
-        * With CONFIG_ARCH_HAS_CPU_RELAX, C0 is already assigned
-        * an power value of -1.  So we use -2, -3, etc, for other
-        * c-states.
-        */
-       for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++)
-               drv->states[i].power_usage = -1 - i;
-}
-
 static void __cpuidle_driver_init(struct cpuidle_driver *drv)
 {
        drv->refcnt = 0;
-
-       if (!drv->power_specified)
-               set_power_states(drv);
 }

 static int __cpuidle_register_driver(struct cpuidle_driver *drv, int cpu)

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 2efee27..14eb11f 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c

@@ -312,7 +312,6 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
        struct menu_device *data = &__get_cpu_var(menu_devices);
        int latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
-       int power_usage = -1;
        int i;
        int multiplier;
        struct timespec t;

@@ -383,11 +382,8 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev)
                if (s->exit_latency * multiplier > data->predicted_us)
                        continue;

-               if (s->power_usage < power_usage) {
-                       power_usage = s->power_usage;
-                       data->last_state_idx = i;
-                       data->exit_us = s->exit_latency;
-               }
+               data->last_state_idx = i;
+               data->exit_us = s->exit_latency;
        }

        /* not deepest C-state chosen for low predicted residency */

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 3711b34..24cd103 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h

@@ -126,9 +126,9 @@ struct cpuidle_driver {
        struct module           *owner;
        int                     refcnt;

-       unsigned int            power_specified:1;
        /* set to 1 to use the core cpuidle time keeping (for all states). */
        unsigned int            en_core_tk_irqen:1;
+       /* states array must be ordered in decreasing power consumption */
        struct cpuidle_state    states[CPUIDLE_STATE_MAX];
        int                     state_count;
        int                     safe_state_index;
--

1.7.5.4

-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

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Hi,

On 11/12/2012 09:26 PM, Daniel Lezcano wrote:

I guess you meant drv->states[i].enter_dead

+			return drv->states[i].enter_dead(dev, i);

--
Francesco

On 11/18/2012 09:40 AM, Francesco Lavra wrote:

Hi,

On 11/12/2012 09:26 PM, Daniel Lezcano wrote:

quoted

This patch follows the discussion about reinitializing the power usage
when a C-state is added/removed.

 https://lkml.org/lkml/2012/10/16/518

We realized the power usage field is never filled and when it is
filled for tegra, the power_specified flag is not set making all these
values to be resetted when the driver is initialized with the set_power_state
function.

Julius and I feel this is over-engineered and the power_specified
flag could be simply removed and continue assuming the states are
backward sorted.

The menu governor select function is simplified as the power is ordered.
Actually the condition is always true with the current code.

The cpuidle_play_dead function is also simplified by doing a reverse lookup
on the array.

The set_power_states function is removed as it does no make sense anymore.

Signed-off-by: Daniel Lezcano <redacted>
---
 drivers/cpuidle/cpuidle.c        |   17 ++++-------------
 drivers/cpuidle/driver.c         |   25 -------------------------
 drivers/cpuidle/governors/menu.c |    8 ++------
 include/linux/cpuidle.h          |    2 +-
 4 files changed, 7 insertions(+), 45 deletions(-)

diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 711dd83..f983262 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c

@@ -69,24 +69,15 @@ int cpuidle_play_dead(void)
 {
 	struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices);
 	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);
-	int i, dead_state = -1;
-	int power_usage = -1;
+	int i;
 
 	if (!drv)
 		return -ENODEV;
 
 	/* Find lowest-power state that supports long-term idle */
-	for (i = CPUIDLE_DRIVER_STATE_START; i < drv->state_count; i++) {
-		struct cpuidle_state *s = &drv->states[i];
-
-		if (s->power_usage < power_usage && s->enter_dead) {
-			power_usage = s->power_usage;
-			dead_state = i;
-		}
-	}
-
-	if (dead_state != -1)
-		return drv->states[dead_state].enter_dead(dev, dead_state);
+	for (i = drv->state_count; i >= CPUIDLE_DRIVER_STATE_START; i--)
+		if (drv->states[i].play_dead)

I guess you meant drv->states[i].enter_dead

Yep :)



-- 
 <http://www.linaro.org/> Linaro.org │ Open source software for ARM SoCs

Follow Linaro:  <http://www.facebook.com/pages/Linaro> Facebook |
<http://twitter.com/#!/linaroorg> Twitter |
<http://www.linaro.org/linaro-blog/> Blog

Hi,

What is the current status of this? Daniel, do you think you have got
enough feedback to submit a definitive patch for this? Rafael, would
you approve of such a change?

The bug with dynamically added C-states that is tied to this still
hurts the battery life for some users across all distros every day, so
I think it would be valuable to get a consistent solution into the
mainline soon before everyone has to roll their own.

On 11/12/2012 09:26 PM, Daniel Lezcano wrote:

This patch follows the discussion about reinitializing the power usage
when a C-state is added/removed.

 https://lkml.org/lkml/2012/10/16/518

We realized the power usage field is never filled and when it is
filled for tegra, the power_specified flag is not set making all these
values to be resetted when the driver is initialized with the set_power_state
function.

Julius and I feel this is over-engineered and the power_specified
flag could be simply removed and continue assuming the states are
backward sorted.

The menu governor select function is simplified as the power is ordered.
Actually the condition is always true with the current code.

The cpuidle_play_dead function is also simplified by doing a reverse lookup
on the array.

The set_power_states function is removed as it does no make sense anymore.

Signed-off-by: Daniel Lezcano <redacted>
---
 drivers/cpuidle/cpuidle.c        |   17 ++++-------------
 drivers/cpuidle/driver.c         |   25 -------------------------
 drivers/cpuidle/governors/menu.c |    8 ++------
 include/linux/cpuidle.h          |    2 +-
 4 files changed, 7 insertions(+), 45 deletions(-)

On Monday, December 10, 2012 11:09:58 AM Julius Werner wrote:

Hi,

What is the current status of this? Daniel, do you think you have got
enough feedback to submit a definitive patch for this? Rafael, would
you approve of such a change?

I need to talk to Len about that before I give you a reliable answer.

Thanks,
Rafael

The bug with dynamically added C-states that is tied to this still
hurts the battery life for some users across all distros every day, so
I think it would be valuable to get a consistent solution into the
mainline soon before everyone has to roll their own.

On 11/12/2012 09:26 PM, Daniel Lezcano wrote:

quoted

This patch follows the discussion about reinitializing the power usage
when a C-state is added/removed.

 https://lkml.org/lkml/2012/10/16/518

We realized the power usage field is never filled and when it is
filled for tegra, the power_specified flag is not set making all these
values to be resetted when the driver is initialized with the set_power_state
function.

Julius and I feel this is over-engineered and the power_specified
flag could be simply removed and continue assuming the states are
backward sorted.

The menu governor select function is simplified as the power is ordered.
Actually the condition is always true with the current code.

The cpuidle_play_dead function is also simplified by doing a reverse lookup
on the array.

The set_power_states function is removed as it does no make sense anymore.

Signed-off-by: Daniel Lezcano <redacted>
---
 drivers/cpuidle/cpuidle.c        |   17 ++++-------------
 drivers/cpuidle/driver.c         |   25 -------------------------
 drivers/cpuidle/governors/menu.c |    8 ++------
 include/linux/cpuidle.h          |    2 +-
 4 files changed, 7 insertions(+), 45 deletions(-)

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

On 12/10/2012 08:09 PM, Julius Werner wrote:

Hi,

What is the current status of this? Daniel, do you think you have got
enough feedback to submit a definitive patch for this? 

Yes, I have a definitive patch. I will resend it tomorrow.

Thanks
  -- Daniel