[PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Stratos Karafotis]

Function __cpufreq_driver_target checks if target_freq is within
policy->min and policy->max range. generic_powersave_bias_target also
checks if target_freq is valid through cpufreq_frequency_table_target
call. So, drop the unnecessary duplicate check in *_check_cpu functions.

Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
---
 drivers/cpufreq/cpufreq_conservative.c | 4 ----
 drivers/cpufreq/cpufreq_ondemand.c     | 3 ---
 2 files changed, 7 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index 7f67a75..f62d822 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -67,8 +67,6 @@ static void cs_check_cpu(int cpu, unsigned int load)
 			return;
 
 		dbs_info->requested_freq += get_freq_target(cs_tuners, policy);
-		if (dbs_info->requested_freq > policy->max)
-			dbs_info->requested_freq = policy->max;
 
 		__cpufreq_driver_target(policy, dbs_info->requested_freq,
 			CPUFREQ_RELATION_H);
@@ -89,8 +87,6 @@ static void cs_check_cpu(int cpu, unsigned int load)
 			return;
 
 		dbs_info->requested_freq -= get_freq_target(cs_tuners, policy);
-		if (dbs_info->requested_freq < policy->min)
-			dbs_info->requested_freq = policy->min;
 
 		__cpufreq_driver_target(policy, dbs_info->requested_freq,
 				CPUFREQ_RELATION_L);
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 87f3305..32f26f6 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -177,9 +177,6 @@ static void od_check_cpu(int cpu, unsigned int load)
 		/* No longer fully busy, reset rate_mult */
 		dbs_info->rate_mult = 1;
 
-		if (freq_next < policy->min)
-			freq_next = policy->min;
-
 		if (!od_tuners->powersave_bias) {
 			__cpufreq_driver_target(policy, freq_next,
 					CPUFREQ_RELATION_L);
-- 
1.8.3.1

Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Viresh Kumar]

On 27 August 2013 00:07, Stratos Karafotis <stratosk@semaphore.gr> wrote:
>  drivers/cpufreq/cpufreq_conservative.c | 4 ----

Get rid of few more checks..

/* if we are already at full speed then break out early */
if (dbs_info->requested_freq == policy->max)
return;


/*
* if we cannot reduce the frequency anymore, break out early
*/
if (policy->cur == policy->min)
return;

Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Stratos Karafotis]

On 08/27/2013 08:57 AM, Viresh Kumar wrote:
> On 27 August 2013 00:07, Stratos Karafotis <stratosk@semaphore.gr> wrote:
>>   drivers/cpufreq/cpufreq_conservative.c | 4 ----
> 
> Get rid of few more checks..
> 
> /* if we are already at full speed then break out early */
> if (dbs_info->requested_freq == policy->max)
> return;
> 
> 
> /*
> * if we cannot reduce the frequency anymore, break out early
> */
> if (policy->cur == policy->min)
> return;
> 

I think we should keep these checks because:

1) They shorten the execution code (there is no unnecessary call of
__cpufreq_driver_target)
2) In case my patch will be accepted, we need them to avoid continuously
increase of dbs_info->requested_freq.With my patch the requested_freq
can temporarily overcome policy->min and policy->max. __cpufreq_driver_target
will select the correct frequency (within policy->min and policy->max).
Then, dbs_cpufreq_notifier will adjust requested_freq.

I hope the logic in 2) to be acceptable.


Thanks,
Stratos

Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Viresh Kumar]

On 27 August 2013 21:16, Stratos Karafotis <stratosk@semaphore.gr> wrote:
> I think we should keep these checks because:
>
> 1) They shorten the execution code (there is no unnecessary call of
> __cpufreq_driver_target)

I don't really count this one.. This is how code is present everywhere in
kernel.. These checks are present in routines and callers don't need to
take care of them..

> 2) In case my patch will be accepted, we need them to avoid continuously
> increase of dbs_info->requested_freq.With my patch the requested_freq
> can temporarily overcome policy->min and policy->max. __cpufreq_driver_target
> will select the correct frequency (within policy->min and policy->max).
> Then, dbs_cpufreq_notifier will adjust requested_freq.

Sorry, I couldn't understand what you meant here :(

Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Stratos Karafotis]

On 08/27/2013 07:07 PM, Viresh Kumar wrote:
> On 27 August 2013 21:16, Stratos Karafotis <stratosk@semaphore.gr> wrote:
>> I think we should keep these checks because:
>>
>> 1) They shorten the execution code (there is no unnecessary call of
>> __cpufreq_driver_target)
>
> I don't really count this one.. This is how code is present everywhere in
> kernel.. These checks are present in routines and callers don't need to
> take care of them..

I mean that if we will get rid of the code you mentioned, we will have
an extra call to function __cpufreq_driver_target in some cases.

>> 2) In case my patch will be accepted, we need them to avoid continuously
>> increase of dbs_info->requested_freq.With my patch the requested_freq
>> can temporarily overcome policy->min and policy->max. __cpufreq_driver_target
>> will select the correct frequency (within policy->min and policy->max).
>> Then, dbs_cpufreq_notifier will adjust requested_freq.
>
> Sorry, I couldn't understand what you meant here :(
>

I'm sorry. Let me try to explain this better.

With my patch, dbs_info->requested_freq will not be capped within
policy->min and policy->max in cs_check_cpu.
So, temporarily it may have a value greater than policy->max
or lower that policy->min.
When we call __cpufreq_driver_target, the correct frequency will be 
selected because __cpufreq_driver_target takes care to adjust the
target frequency within policy range.
But, eventually, dbs_cpufreq_notifier will adjust dbs_info->requested
within policy range, if needed.

If we remove
	if (dbs_info->requested_freq == policy->max)
		return;
and
	if (policy->cur == policy->min)
		return;

request_freq will keep increasing or decreasing in each iteration and
finally will overflow or underflow.

Consider, for example, that in a CPU with policy->max = 1000MHz
the current frequency is 950MHz. With a constant load above
up_threshold, the requested_freq in first iteration will be 1000MHz
and __cpufreq_driver_target will select 1000MHz freq.

In second iteration, requested_freq will be 1050MHz, and 
__cpufreq_driver_target will select 1000MHz. dbs_cpufreq_notifier
will adjust requested_freq back to 1000MHz.

In next iterations, dbs_cpufreq_notifier will not be called, so we
need the above check (dbs_info->requested_freq == policy->max) to
prevent requested_freq to grow arbitrary.

I hope my explanation was better now. :)


Thanks,
Stratos

Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Viresh Kumar]

 27 August 2013 23:04, Stratos Karafotis <stratosk@semaphore.gr> wrote:
> I'm sorry. Let me try to explain this better.

Don't be :)

> With my patch, dbs_info->requested_freq will not be capped within
> policy->min and policy->max in cs_check_cpu.
> So, temporarily it may have a value greater than policy->max
> or lower that policy->min.
> When we call __cpufreq_driver_target, the correct frequency will be selected
> because __cpufreq_driver_target takes care to adjust the
> target frequency within policy range.
> But, eventually, dbs_cpufreq_notifier will adjust dbs_info->requested
> within policy range, if needed.
>
> If we remove
>
>         if (dbs_info->requested_freq == policy->max)
>                 return;
> and
>
>         if (policy->cur == policy->min)
>                 return;
>
> request_freq will keep increasing or decreasing in each iteration and
> finally will overflow or underflow.
>
> Consider, for example, that in a CPU with policy->max = 1000MHz
> the current frequency is 950MHz. With a constant load above
> up_threshold, the requested_freq in first iteration will be 1000MHz
> and __cpufreq_driver_target will select 1000MHz freq.
>
> In second iteration, requested_freq will be 1050MHz, and
> __cpufreq_driver_target will select 1000MHz. dbs_cpufreq_notifier
> will adjust requested_freq back to 1000MHz.
>
> In next iterations, dbs_cpufreq_notifier will not be called, so we
> need the above check (dbs_info->requested_freq == policy->max) to
> prevent requested_freq to grow arbitrary.
>
> I hope my explanation was better now. :)

Yes, your initial patch is fine.

Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range

[Viresh Kumar]

On 27 August 2013 00:07, Stratos Karafotis <stratosk@semaphore.gr> wrote:
> Function __cpufreq_driver_target checks if target_freq is within
> policy->min and policy->max range. generic_powersave_bias_target also
> checks if target_freq is valid through cpufreq_frequency_table_target
> call. So, drop the unnecessary duplicate check in *_check_cpu functions.
>
> Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
> ---
>  drivers/cpufreq/cpufreq_conservative.c | 4 ----
>  drivers/cpufreq/cpufreq_ondemand.c     | 3 ---
>  2 files changed, 7 deletions(-)

Acked-by: Viresh Kumar <viresh.kumar@linaro.org>