RE: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Doug Smythies]

On 2017.11.16 08:11 Thomas Ilsche wrote:
> On 2017-11-09 08:38, Len Brown wrote:
>> From: Len Brown 
>> 
>> While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
>> cpuidle to shallow idle states, there is no simple mechanism
>> to give the hardware permission to enter the deeptest state permitted by 
>> PM_QOS.
>> 
>> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
>> 
>> "cpuidle.use_deepest=Y" can be set at boot-time, and
>> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
>
> This is a good option to have and can conveniently prevent idle power 
> consumption
> issues. But that wouldn't be a reasonable default, would it?
> I still think there is an inherent need for a heuristic and a corresponding
> mitigation to avoid staying in a sleep state too long.

I think so, yes. The potential energy savings, depending on work flow, are 
significant.
For the idle state 0 case, I have some supporting data that I will send on
the other e-mail thread.

... Doug

RE: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Doug Smythies]

On 2017.11.16 08:11 Thomas Ilsche wrote:
> On 2017-11-09 08:38, Len Brown wrote:
>> From: Len Brown 
>> 
>> While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
>> cpuidle to shallow idle states, there is no simple mechanism
>> to give the hardware permission to enter the deeptest state permitted by 
>> PM_QOS.
>> 
>> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
>> 
>> "cpuidle.use_deepest=Y" can be set at boot-time, and
>> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
>
> This is a good option to have and can conveniently prevent idle power 
> consumption
> issues. But that wouldn't be a reasonable default, would it?
> I still think there is an inherent need for a heuristic and a corresponding
> mitigation to avoid staying in a sleep state too long.

I think so, yes. The potential energy savings, depending on work flow, are 
significant.
For the idle state 0 case, I have some supporting data that I will send on
the other e-mail thread.

... Doug

Re: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Thomas Ilsche]

On 2017-11-09 08:38, Len Brown wrote:

From: Len Brown 

While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
cpuidle to shallow idle states, there is no simple mechanism
to give the hardware permission to enter the deeptest state permitted by PM_QOS.

Here we create the "cpuidle.use_deepest" modparam to provide this capability.

"cpuidle.use_deepest=Y" can be set at boot-time, and
/sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.


This is a good option to have and can conveniently prevent idle power 
consumption
issues. But that wouldn't be a reasonable default, would it?
I still think there is an inherent need for a heuristic and a corresponding
mitigation to avoid staying in a sleep state too long.

Best,
Thomas

Re: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Thomas Ilsche]

On 2017-11-09 08:38, Len Brown wrote:

From: Len Brown 

While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
cpuidle to shallow idle states, there is no simple mechanism
to give the hardware permission to enter the deeptest state permitted by PM_QOS.

Here we create the "cpuidle.use_deepest" modparam to provide this capability.

"cpuidle.use_deepest=Y" can be set at boot-time, and
/sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.


This is a good option to have and can conveniently prevent idle power 
consumption
issues. But that wouldn't be a reasonable default, would it?
I still think there is an inherent need for a heuristic and a corresponding
mitigation to avoid staying in a sleep state too long.

Best,
Thomas

RE: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Doug Smythies]

Hi Len,

Other feedback notwithstanding, works fine for me.
Just a small typo type comment:

On 2017.11.08 23:39 Len Brown wrote:

...[snip]...

> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
> 
> "cpuidle.use_deepest=Y" can be set at boot-time, and
> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.

Should be:

/sys/module/cpuidle/parameters/use_deepest

...[snip]...

RE: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Doug Smythies]

Hi Len,

Other feedback notwithstanding, works fine for me.
Just a small typo type comment:

On 2017.11.08 23:39 Len Brown wrote:

...[snip]...

> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
> 
> "cpuidle.use_deepest=Y" can be set at boot-time, and
> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.

Should be:

/sys/module/cpuidle/parameters/use_deepest

...[snip]...

Re: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Vincent Guittot]

Hi Len

On 9 November 2017 at 08:38, Len Brown  wrote:
> From: Len Brown 
>
> While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
> cpuidle to shallow idle states, there is no simple mechanism
> to give the hardware permission to enter the deeptest state permitted by 
> PM_QOS.

and by per device resume latency QoS

>
> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
>
> "cpuidle.use_deepest=Y" can be set at boot-time, and
> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
>
> n.b.
>
> Within the constraints of PM_QOS, this mechanism gives the hardware
> permission to choose the deeptest power savings and highest latency
> state available.  And so choice will depend on the particular hardware.
>
> Also, if PM_QOS is not informed of latency constraints, it can't help.
> In that case, using this mechanism may result in entering high-latency
> states that impact performance.
>
> Signed-off-by: Len Brown 
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  4 
>  drivers/cpuidle/cpuidle.c   | 19 
>  include/linux/cpuidle.h |  7 ++
>  kernel/sched/idle.c | 30 
> +++--
>  4 files changed, 53 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt 
> b/Documentation/admin-guide/kernel-parameters.txt
> index 05496622b4ef..20f70de688bf 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -659,6 +659,10 @@
> cpuidle.off=1   [CPU_IDLE]
> disable the cpuidle sub-system
>
> +   cpuidle.use_deepest=Y   [CPU_IDLE]
> +   Ignore cpuidle governor, always choose deepest
> +   PM_QOS-legal CPU idle power saving state.
> +
> cpufreq.off=1   [CPU_FREQ]
> disable the cpufreq sub-system
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 484cc8909d5c..afee5aab7719 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -34,6 +34,7 @@ LIST_HEAD(cpuidle_detected_devices);
>
>  static int enabled_devices;
>  static int off __read_mostly;
> +static bool use_deepest __read_mostly;
>  static int initialized __read_mostly;
>
>  int cpuidle_disabled(void)
> @@ -116,6 +117,10 @@ void cpuidle_use_deepest_state(bool enable)
> preempt_enable();
>  }
>
> +bool cpuidle_using_deepest_state(void)
> +{
> +   return use_deepest;
> +}
>  /**
>   * cpuidle_find_deepest_state - Find the deepest available idle state.
>   * @drv: cpuidle driver for the given CPU.
> @@ -127,6 +132,19 @@ int cpuidle_find_deepest_state(struct cpuidle_driver 
> *drv,
> return find_deepest_state(drv, dev, UINT_MAX, 0, false);
>  }
>
> +/**
> + * cpuidle_find_deepest_state_qos - Find the deepest available idle state.
> + * @drv: cpuidle driver for the given CPU.
> + * @dev: cpuidle device for the given CPU.
> + * Honors PM_QOS
> + */
> +int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> +  struct cpuidle_device *dev)
> +{
> +   return find_deepest_state(drv, dev,
> +   pm_qos_request(PM_QOS_CPU_DMA_LATENCY), 0, false);

You should also take into account per device latency  like in menu governor:
dev_pm_qos_raw_read_value(device);


> +}
> +
>  #ifdef CONFIG_SUSPEND
>  static void enter_s2idle_proper(struct cpuidle_driver *drv,
> struct cpuidle_device *dev, int index)
> @@ -681,4 +699,5 @@ static int __init cpuidle_init(void)
>  }
>
>  module_param(off, int, 0444);
> +module_param(use_deepest, bool, 0644);
>  core_initcall(cpuidle_init);
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 8f7788d23b57..e3c2c9d1898f 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -198,19 +198,26 @@ static inline struct cpuidle_device 
> *cpuidle_get_device(void) {return NULL; }
>  #ifdef CONFIG_CPU_IDLE
>  extern int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
>   struct cpuidle_device *dev);
> +extern int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev);
>  extern int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
> struct cpuidle_device *dev);
>  extern void cpuidle_use_deepest_state(bool enable);
> +extern bool cpuidle_using_deepest_state(void);
>  #else
>  static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
>  struct cpuidle_device *dev)
>  {return -ENODEV; }
> +static inline int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> +struct 

Re: [PATCH] cpuidle: Add "cpuidle.use_deepest" to bypass governor and allow HW to go deep

[Vincent Guittot]

Hi Len

On 9 November 2017 at 08:38, Len Brown  wrote:
> From: Len Brown 
>
> While there are several mechanisms (cmdline, sysfs, PM_QOS) to limit
> cpuidle to shallow idle states, there is no simple mechanism
> to give the hardware permission to enter the deeptest state permitted by 
> PM_QOS.

and by per device resume latency QoS

>
> Here we create the "cpuidle.use_deepest" modparam to provide this capability.
>
> "cpuidle.use_deepest=Y" can be set at boot-time, and
> /sys/module/cpuidle/use_deepest can be modified (with Y/N) at run-time.
>
> n.b.
>
> Within the constraints of PM_QOS, this mechanism gives the hardware
> permission to choose the deeptest power savings and highest latency
> state available.  And so choice will depend on the particular hardware.
>
> Also, if PM_QOS is not informed of latency constraints, it can't help.
> In that case, using this mechanism may result in entering high-latency
> states that impact performance.
>
> Signed-off-by: Len Brown 
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  4 
>  drivers/cpuidle/cpuidle.c   | 19 
>  include/linux/cpuidle.h |  7 ++
>  kernel/sched/idle.c | 30 
> +++--
>  4 files changed, 53 insertions(+), 7 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt 
> b/Documentation/admin-guide/kernel-parameters.txt
> index 05496622b4ef..20f70de688bf 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -659,6 +659,10 @@
> cpuidle.off=1   [CPU_IDLE]
> disable the cpuidle sub-system
>
> +   cpuidle.use_deepest=Y   [CPU_IDLE]
> +   Ignore cpuidle governor, always choose deepest
> +   PM_QOS-legal CPU idle power saving state.
> +
> cpufreq.off=1   [CPU_FREQ]
> disable the cpufreq sub-system
>
> diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
> index 484cc8909d5c..afee5aab7719 100644
> --- a/drivers/cpuidle/cpuidle.c
> +++ b/drivers/cpuidle/cpuidle.c
> @@ -34,6 +34,7 @@ LIST_HEAD(cpuidle_detected_devices);
>
>  static int enabled_devices;
>  static int off __read_mostly;
> +static bool use_deepest __read_mostly;
>  static int initialized __read_mostly;
>
>  int cpuidle_disabled(void)
> @@ -116,6 +117,10 @@ void cpuidle_use_deepest_state(bool enable)
> preempt_enable();
>  }
>
> +bool cpuidle_using_deepest_state(void)
> +{
> +   return use_deepest;
> +}
>  /**
>   * cpuidle_find_deepest_state - Find the deepest available idle state.
>   * @drv: cpuidle driver for the given CPU.
> @@ -127,6 +132,19 @@ int cpuidle_find_deepest_state(struct cpuidle_driver 
> *drv,
> return find_deepest_state(drv, dev, UINT_MAX, 0, false);
>  }
>
> +/**
> + * cpuidle_find_deepest_state_qos - Find the deepest available idle state.
> + * @drv: cpuidle driver for the given CPU.
> + * @dev: cpuidle device for the given CPU.
> + * Honors PM_QOS
> + */
> +int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> +  struct cpuidle_device *dev)
> +{
> +   return find_deepest_state(drv, dev,
> +   pm_qos_request(PM_QOS_CPU_DMA_LATENCY), 0, false);

You should also take into account per device latency  like in menu governor:
dev_pm_qos_raw_read_value(device);


> +}
> +
>  #ifdef CONFIG_SUSPEND
>  static void enter_s2idle_proper(struct cpuidle_driver *drv,
> struct cpuidle_device *dev, int index)
> @@ -681,4 +699,5 @@ static int __init cpuidle_init(void)
>  }
>
>  module_param(off, int, 0444);
> +module_param(use_deepest, bool, 0644);
>  core_initcall(cpuidle_init);
> diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
> index 8f7788d23b57..e3c2c9d1898f 100644
> --- a/include/linux/cpuidle.h
> +++ b/include/linux/cpuidle.h
> @@ -198,19 +198,26 @@ static inline struct cpuidle_device 
> *cpuidle_get_device(void) {return NULL; }
>  #ifdef CONFIG_CPU_IDLE
>  extern int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
>   struct cpuidle_device *dev);
> +extern int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> + struct cpuidle_device *dev);
>  extern int cpuidle_enter_s2idle(struct cpuidle_driver *drv,
> struct cpuidle_device *dev);
>  extern void cpuidle_use_deepest_state(bool enable);
> +extern bool cpuidle_using_deepest_state(void);
>  #else
>  static inline int cpuidle_find_deepest_state(struct cpuidle_driver *drv,
>  struct cpuidle_device *dev)
>  {return -ENODEV; }
> +static inline int cpuidle_find_deepest_state_qos(struct cpuidle_driver *drv,
> +struct cpuidle_device *dev)
> +{return -ENODEV; }
>  static inline