[PATCH v2 0/2] Avoid calling cpu_pm functions for retention idle states

[PATCH v2 0/2] Avoid calling cpu_pm functions for retention idle states

[Prashanth Prakash]

CPU_PM_CPU_IDLE_ENTER() treats all idle states whose idx != 0 as a
state that loses some context, but we can have deeper idle states that
doesn't lose any software context. If a CPU is entering such a low power
idle state where it retains the context, then there is no need to call
cpu_pm_enter()/cpu_pm_exit().

Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
drivers when they are entering retention state. By not calling cpu_pm_enter
and cpu_pm_exit we reduce the latency involved in entering and exiting
the retention states.

On ARM64 based Qualcomm server platform we measured below overhead for
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
Overhead of cpu_pm_enter - 1.2us(Average), 6.5us(Max)
Overhead of cpu_pm_exit  - 3.1us(Average), 11.1us(Max)

Listed below are 5 functions that were notified on ENTER/EXIT on the
test platform:
      gic_cpu_pm_notifier
      arch_timer_cpu_pm_notify
      cpu_pm_pmu_notify
      hyp_init_cpu_pm_notifier
      fpsimd_cpu_pm_notifier

Prashanth Prakash (2):
  cpuidle: Add new macro to enter a retention idle state
  ARM64 / cpuidle: Use new cpuidle macro for entering retention state

Changes in v2:
 - Reordered cpuidle.h macros for better readablity (Rafael)

 arch/arm64/kernel/cpuidle.c |  8 +++++++-
 include/linux/cpuidle.h     | 40 ++++++++++++++++++++++++----------------
 2 files changed, 31 insertions(+), 17 deletions(-)

-- 
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

[PATCH v2 0/2] Avoid calling cpu_pm functions for retention idle states

[Prashanth Prakash]

CPU_PM_CPU_IDLE_ENTER() treats all idle states whose idx != 0 as a
state that loses some context, but we can have deeper idle states that
doesn't lose any software context. If a CPU is entering such a low power
idle state where it retains the context, then there is no need to call
cpu_pm_enter()/cpu_pm_exit().

Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
drivers when they are entering retention state. By not calling cpu_pm_enter
and cpu_pm_exit we reduce the latency involved in entering and exiting
the retention states.

On ARM64 based Qualcomm server platform we measured below overhead for
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
Overhead of cpu_pm_enter - 1.2us(Average), 6.5us(Max)
Overhead of cpu_pm_exit  - 3.1us(Average), 11.1us(Max)

Listed below are 5 functions that were notified on ENTER/EXIT on the
test platform:
      gic_cpu_pm_notifier
      arch_timer_cpu_pm_notify
      cpu_pm_pmu_notify
      hyp_init_cpu_pm_notifier
      fpsimd_cpu_pm_notifier

Prashanth Prakash (2):
  cpuidle: Add new macro to enter a retention idle state
  ARM64 / cpuidle: Use new cpuidle macro for entering retention state

Changes in v2:
 - Reordered cpuidle.h macros for better readablity (Rafael)

 arch/arm64/kernel/cpuidle.c |  8 +++++++-
 include/linux/cpuidle.h     | 40 ++++++++++++++++++++++++----------------
 2 files changed, 31 insertions(+), 17 deletions(-)

-- 
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

[PATCH v2 1/2] cpuidle: Add new macro to enter a retention idle state

[Prashanth Prakash]

If a CPU is entering a low power idle state where it doesn't lose any
context, then there is no need to call cpu_pm_enter()/cpu_pm_exit().
Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
drivers when they are entering retention state. By not calling
cpu_pm_enter and cpu_pm_exit we reduce the latency involved in
entering and exiting the retention idle states.

On ARM64 based Qualcomm Server Platform we measured below overhead for
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
        Average overhead of cpu_pm_enter - 1.2us
        Average overhead of cpu_pm_exit  - 3.1us

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
---
 include/linux/cpuidle.h | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 8f7788d..871f9e2 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -257,22 +257,30 @@ static inline int cpuidle_register_governor(struct cpuidle_governor *gov)
 {return 0;}
 #endif
 
-#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx)	\
-({								\
-	int __ret;						\
-								\
-	if (!idx) {						\
-		cpu_do_idle();					\
-		return idx;					\
-	}							\
-								\
-	__ret = cpu_pm_enter();					\
-	if (!__ret) {						\
-		__ret = low_level_idle_enter(idx);		\
-		cpu_pm_exit();					\
-	}							\
-								\
-	__ret ? -1 : idx;					\
+#define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, is_retention) \
+({									\
+	int __ret = 0;							\
+									\
+	if (!idx) {							\
+		cpu_do_idle();						\
+		return idx;						\
+	}								\
+									\
+	if (!is_retention)						\
+		__ret =  cpu_pm_enter();				\
+	if (!__ret) {							\
+		__ret = low_level_idle_enter(idx);			\
+		if (!is_retention)					\
+			cpu_pm_exit();					\
+	}								\
+									\
+	__ret ? -1 : idx;						\
 })
 
+#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx)	\
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, 0)
+
+#define CPU_PM_CPU_IDLE_ENTER_RETENTION(low_level_idle_enter, idx)	\
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, 1)
+
 #endif /* _LINUX_CPUIDLE_H */
-- 
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

[PATCH v2 1/2] cpuidle: Add new macro to enter a retention idle state

[Prashanth Prakash]

If a CPU is entering a low power idle state where it doesn't lose any
context, then there is no need to call cpu_pm_enter()/cpu_pm_exit().
Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
drivers when they are entering retention state. By not calling
cpu_pm_enter and cpu_pm_exit we reduce the latency involved in
entering and exiting the retention idle states.

On ARM64 based Qualcomm Server Platform we measured below overhead for
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
        Average overhead of cpu_pm_enter - 1.2us
        Average overhead of cpu_pm_exit  - 3.1us

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
---
 include/linux/cpuidle.h | 40 ++++++++++++++++++++++++----------------
 1 file changed, 24 insertions(+), 16 deletions(-)

diff --git a/include/linux/cpuidle.h b/include/linux/cpuidle.h
index 8f7788d..871f9e2 100644
--- a/include/linux/cpuidle.h
+++ b/include/linux/cpuidle.h
@@ -257,22 +257,30 @@ static inline int cpuidle_register_governor(struct cpuidle_governor *gov)
 {return 0;}
 #endif
 
-#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx)	\
-({								\
-	int __ret;						\
-								\
-	if (!idx) {						\
-		cpu_do_idle();					\
-		return idx;					\
-	}							\
-								\
-	__ret = cpu_pm_enter();					\
-	if (!__ret) {						\
-		__ret = low_level_idle_enter(idx);		\
-		cpu_pm_exit();					\
-	}							\
-								\
-	__ret ? -1 : idx;					\
+#define __CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, is_retention) \
+({									\
+	int __ret = 0;							\
+									\
+	if (!idx) {							\
+		cpu_do_idle();						\
+		return idx;						\
+	}								\
+									\
+	if (!is_retention)						\
+		__ret =  cpu_pm_enter();				\
+	if (!__ret) {							\
+		__ret = low_level_idle_enter(idx);			\
+		if (!is_retention)					\
+			cpu_pm_exit();					\
+	}								\
+									\
+	__ret ? -1 : idx;						\
 })
 
+#define CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx)	\
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, 0)
+
+#define CPU_PM_CPU_IDLE_ENTER_RETENTION(low_level_idle_enter, idx)	\
+	__CPU_PM_CPU_IDLE_ENTER(low_level_idle_enter, idx, 1)
+
 #endif /* _LINUX_CPUIDLE_H */
-- 
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

[PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Prashanth Prakash]

CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
paths we can reduce the latency involved in entering and exiting
the low power idle state.

On ARM64 based Qualcomm server platform we measured below overhead
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
	Average overhead of cpu_pm_enter - 1.2us
	Average overhead of cpu_pm_exit  - 3.1us

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
---
 arch/arm64/kernel/cpuidle.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
index fd69108..f2d1381 100644
--- a/arch/arm64/kernel/cpuidle.c
+++ b/arch/arm64/kernel/cpuidle.c
@@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
 
 #include <acpi/processor.h>
 
+#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
+
 int acpi_processor_ffh_lpi_probe(unsigned int cpu)
 {
 	return arm_cpuidle_init(cpu);
@@ -54,6 +56,10 @@ int acpi_processor_ffh_lpi_probe(unsigned int cpu)
 
 int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
 {
-	return CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, lpi->index);
+	if (ARM64_LPI_IS_RETENTION_STATE(lpi->arch_flags))
+		return CPU_PM_CPU_IDLE_ENTER_RETENTION(arm_cpuidle_suspend,
+						lpi->index);
+	else
+		return CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, lpi->index);
 }
 #endif
-- 
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

[PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Prashanth Prakash]

CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
paths we can reduce the latency involved in entering and exiting
the low power idle state.

On ARM64 based Qualcomm server platform we measured below overhead
for calling cpu_pm_enter and cpu_pm_exit for retention states.

workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
	Average overhead of cpu_pm_enter - 1.2us
	Average overhead of cpu_pm_exit  - 3.1us

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
---
 arch/arm64/kernel/cpuidle.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
index fd69108..f2d1381 100644
--- a/arch/arm64/kernel/cpuidle.c
+++ b/arch/arm64/kernel/cpuidle.c
@@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
 
 #include <acpi/processor.h>
 
+#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
+
 int acpi_processor_ffh_lpi_probe(unsigned int cpu)
 {
 	return arm_cpuidle_init(cpu);
@@ -54,6 +56,10 @@ int acpi_processor_ffh_lpi_probe(unsigned int cpu)
 
 int acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
 {
-	return CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, lpi->index);
+	if (ARM64_LPI_IS_RETENTION_STATE(lpi->arch_flags))
+		return CPU_PM_CPU_IDLE_ENTER_RETENTION(arm_cpuidle_suspend,
+						lpi->index);
+	else
+		return CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, lpi->index);
 }
 #endif
-- 
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.

Re: [PATCH v2 1/2] cpuidle: Add new macro to enter a retention idle state

[Sudeep Holla]

On 09/11/17 00:38, Prashanth Prakash wrote:
> If a CPU is entering a low power idle state where it doesn't lose any
> context, then there is no need to call cpu_pm_enter()/cpu_pm_exit().
> Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
> drivers when they are entering retention state. By not calling
> cpu_pm_enter and cpu_pm_exit we reduce the latency involved in
> entering and exiting the retention idle states.
> 
> On ARM64 based Qualcomm Server Platform we measured below overhead for
> for calling cpu_pm_enter and cpu_pm_exit for retention states.
> 
> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
>         Average overhead of cpu_pm_enter - 1.2us
>         Average overhead of cpu_pm_exit  - 3.1us
> 

Just add a description to inform that if retention is enabled,
it's assumed to be full retention(IOW no state needs to be
saved/restored) and hence the CPU PM notifiers are not called.
We may need to change this in case we need to support partial
retention states in future.

Other than that,

Acked-by: Sudeep Holla <sudeep.holla@arm.com>

-- 
Regards,
Sudeep

[PATCH v2 1/2] cpuidle: Add new macro to enter a retention idle state

[Sudeep Holla]

On 09/11/17 00:38, Prashanth Prakash wrote:
> If a CPU is entering a low power idle state where it doesn't lose any
> context, then there is no need to call cpu_pm_enter()/cpu_pm_exit().
> Add a new macro(CPU_PM_CPU_IDLE_ENTER_RETENTION) to be used by cpuidle
> drivers when they are entering retention state. By not calling
> cpu_pm_enter and cpu_pm_exit we reduce the latency involved in
> entering and exiting the retention idle states.
> 
> On ARM64 based Qualcomm Server Platform we measured below overhead for
> for calling cpu_pm_enter and cpu_pm_exit for retention states.
> 
> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
>         Average overhead of cpu_pm_enter - 1.2us
>         Average overhead of cpu_pm_exit  - 3.1us
> 

Just add a description to inform that if retention is enabled,
it's assumed to be full retention(IOW no state needs to be
saved/restored) and hence the CPU PM notifiers are not called.
We may need to change this in case we need to support partial
retention states in future.

Other than that,

Acked-by: Sudeep Holla <sudeep.holla@arm.com>

-- 
Regards,
Sudeep

Re: [PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Sudeep Holla]

On 09/11/17 00:38, Prashanth Prakash wrote:
> CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
> cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
> paths we can reduce the latency involved in entering and exiting
> the low power idle state.
> 
> On ARM64 based Qualcomm server platform we measured below overhead
> for calling cpu_pm_enter and cpu_pm_exit for retention states.
> 
> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
> 	Average overhead of cpu_pm_enter - 1.2us
> 	Average overhead of cpu_pm_exit  - 3.1us
> 
> Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
> ---
>  arch/arm64/kernel/cpuidle.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
> index fd69108..f2d1381 100644
> --- a/arch/arm64/kernel/cpuidle.c
> +++ b/arch/arm64/kernel/cpuidle.c
> @@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
>  
>  #include <acpi/processor.h>
>  
> +#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
> +

This is fine, but just to be safer, is it better to check for all
flags to be set as we can't/don't support any partial retention modes.

Just curious, how is retention handled on mobile parts. I guess mainline
is not important on those parts, but add a note in the commit message
that we can make it ACPI agnostic and PSCI param dependent if needed.

-- 
Regards,
Sudeep

[PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Sudeep Holla]

On 09/11/17 00:38, Prashanth Prakash wrote:
> CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
> cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
> paths we can reduce the latency involved in entering and exiting
> the low power idle state.
> 
> On ARM64 based Qualcomm server platform we measured below overhead
> for calling cpu_pm_enter and cpu_pm_exit for retention states.
> 
> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
> 	Average overhead of cpu_pm_enter - 1.2us
> 	Average overhead of cpu_pm_exit  - 3.1us
> 
> Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
> ---
>  arch/arm64/kernel/cpuidle.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
> index fd69108..f2d1381 100644
> --- a/arch/arm64/kernel/cpuidle.c
> +++ b/arch/arm64/kernel/cpuidle.c
> @@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
>  
>  #include <acpi/processor.h>
>  
> +#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
> +

This is fine, but just to be safer, is it better to check for all
flags to be set as we can't/don't support any partial retention modes.

Just curious, how is retention handled on mobile parts. I guess mainline
is not important on those parts, but add a note in the commit message
that we can make it ACPI agnostic and PSCI param dependent if needed.

-- 
Regards,
Sudeep

Re: [PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Prakash, Prashanth]

On 11/13/2017 5:33 AM, Sudeep Holla wrote:
>
> On 09/11/17 00:38, Prashanth Prakash wrote:
>> CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
>> cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
>> paths we can reduce the latency involved in entering and exiting
>> the low power idle state.
>>
>> On ARM64 based Qualcomm server platform we measured below overhead
>> for calling cpu_pm_enter and cpu_pm_exit for retention states.
>>
>> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
>> 	Average overhead of cpu_pm_enter - 1.2us
>> 	Average overhead of cpu_pm_exit  - 3.1us
>>
>> Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
>> ---
>>  arch/arm64/kernel/cpuidle.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
>> index fd69108..f2d1381 100644
>> --- a/arch/arm64/kernel/cpuidle.c
>> +++ b/arch/arm64/kernel/cpuidle.c
>> @@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
>>  
>>  #include <acpi/processor.h>
>>  
>> +#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
>> +
> This is fine, but just to be safer, is it better to check for all
> flags to be set as we can't/don't support any partial retention modes.
I am not sure I completely understand.

If any bit is set in arch_flags, then we lose the context corresponding to that bit, so
a full retention state will have no bit set, so that's what we are checking for.
Or am i missing something?

Thanks,
Prashanth

[PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Prakash, Prashanth]

On 11/13/2017 5:33 AM, Sudeep Holla wrote:
>
> On 09/11/17 00:38, Prashanth Prakash wrote:
>> CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
>> cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
>> paths we can reduce the latency involved in entering and exiting
>> the low power idle state.
>>
>> On ARM64 based Qualcomm server platform we measured below overhead
>> for calling cpu_pm_enter and cpu_pm_exit for retention states.
>>
>> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
>> 	Average overhead of cpu_pm_enter - 1.2us
>> 	Average overhead of cpu_pm_exit  - 3.1us
>>
>> Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
>> ---
>>  arch/arm64/kernel/cpuidle.c | 8 +++++++-
>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
>> index fd69108..f2d1381 100644
>> --- a/arch/arm64/kernel/cpuidle.c
>> +++ b/arch/arm64/kernel/cpuidle.c
>> @@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
>>  
>>  #include <acpi/processor.h>
>>  
>> +#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
>> +
> This is fine, but just to be safer, is it better to check for all
> flags to be set as we can't/don't support any partial retention modes.
I am not sure I completely understand.

If any bit is set in arch_flags, then we lose the context corresponding to that bit, so
a full retention state will have no bit set, so that's what we are checking for.
Or am i missing something?

Thanks,
Prashanth

Re: [PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Sudeep Holla]

On 14/11/17 16:15, Prakash, Prashanth wrote:
> 
> 
> On 11/13/2017 5:33 AM, Sudeep Holla wrote:
>>
>> On 09/11/17 00:38, Prashanth Prakash wrote:
>>> CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
>>> cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
>>> paths we can reduce the latency involved in entering and exiting
>>> the low power idle state.
>>>
>>> On ARM64 based Qualcomm server platform we measured below overhead
>>> for calling cpu_pm_enter and cpu_pm_exit for retention states.
>>>
>>> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
>>> 	Average overhead of cpu_pm_enter - 1.2us
>>> 	Average overhead of cpu_pm_exit  - 3.1us
>>>
>>> Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
>>> ---
>>>  arch/arm64/kernel/cpuidle.c | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
>>> index fd69108..f2d1381 100644
>>> --- a/arch/arm64/kernel/cpuidle.c
>>> +++ b/arch/arm64/kernel/cpuidle.c
>>> @@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
>>>  
>>>  #include <acpi/processor.h>
>>>  
>>> +#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
>>> +
>> This is fine, but just to be safer, is it better to check for all
>> flags to be set as we can't/don't support any partial retention modes.
> I am not sure I completely understand.
> 
> If any bit is set in arch_flags, then we lose the context corresponding to that bit, so
> a full retention state will have no bit set, so that's what we are checking for.
> Or am i missing something?
> 

Ah you are right, I somehow misinterpreted the flags exactly to be
opposite(i.e. state retained) rather than state lost, sorry for the noise.

-- 
Regards,
Sudeep

[PATCH v2 2/2] ARM64 / cpuidle: Use new cpuidle macro for entering retention state

[Sudeep Holla]

On 14/11/17 16:15, Prakash, Prashanth wrote:
> 
> 
> On 11/13/2017 5:33 AM, Sudeep Holla wrote:
>>
>> On 09/11/17 00:38, Prashanth Prakash wrote:
>>> CPU_PM_CPU_IDLE_ENTER_RETENTION skips calling cpu_pm_enter() and
>>> cpu_pm_exit(). By not calling cpu_pm functions in idle entry/exit
>>> paths we can reduce the latency involved in entering and exiting
>>> the low power idle state.
>>>
>>> On ARM64 based Qualcomm server platform we measured below overhead
>>> for calling cpu_pm_enter and cpu_pm_exit for retention states.
>>>
>>> workload: stress --hdd #CPUs --hdd-bytes 32M  -t 30
>>> 	Average overhead of cpu_pm_enter - 1.2us
>>> 	Average overhead of cpu_pm_exit  - 3.1us
>>>
>>> Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
>>> ---
>>>  arch/arm64/kernel/cpuidle.c | 8 +++++++-
>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/arm64/kernel/cpuidle.c b/arch/arm64/kernel/cpuidle.c
>>> index fd69108..f2d1381 100644
>>> --- a/arch/arm64/kernel/cpuidle.c
>>> +++ b/arch/arm64/kernel/cpuidle.c
>>> @@ -47,6 +47,8 @@ int arm_cpuidle_suspend(int index)
>>>  
>>>  #include <acpi/processor.h>
>>>  
>>> +#define ARM64_LPI_IS_RETENTION_STATE(arch_flags) (!(arch_flags))
>>> +
>> This is fine, but just to be safer, is it better to check for all
>> flags to be set as we can't/don't support any partial retention modes.
> I am not sure I completely understand.
> 
> If any bit is set in arch_flags, then we lose the context corresponding to that bit, so
> a full retention state will have no bit set, so that's what we are checking for.
> Or am i missing something?
> 

Ah you are right, I somehow misinterpreted the flags exactly to be
opposite(i.e. state retained) rather than state lost, sorry for the noise.

-- 
Regards,
Sudeep