linux-kernel - Re: [PATCH V2 3/5] cpuidle: idle: menu: Don't reflect when a state selection failed

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Date:	Tue, 28 Oct 2014 19:28:02 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Preeti Murthy <preeti.lkml@...il.com>
CC:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	patches@...aro.org, Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH V2 3/5] cpuidle: idle: menu: Don't reflect when a state
 selection failed

On 10/28/2014 08:01 AM, Preeti Murthy wrote:
> On Thu, Oct 23, 2014 at 2:31 PM, Daniel Lezcano
> <daniel.lezcano@...aro.org> wrote:
>> In the current code, the check to reflect or not the outcoming state is done
>> against the idle state which has been chosen and its value.
>>
>> Instead of doing a check in each of the reflect functions, just don't call reflect
>> if something went wrong in the idle path.
>>
>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>> Acked-by: Nicolas Pitre <nico@...aro.org>
>> ---
>>   drivers/cpuidle/governors/ladder.c | 3 +--
>>   drivers/cpuidle/governors/menu.c   | 4 +---
>>   kernel/sched/idle.c                | 3 ++-
>>   3 files changed, 4 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/cpuidle/governors/ladder.c b/drivers/cpuidle/governors/ladder.c
>> index fb396d6..c0b36a8 100644
>> --- a/drivers/cpuidle/governors/ladder.c
>> +++ b/drivers/cpuidle/governors/ladder.c
>> @@ -165,8 +165,7 @@ static int ladder_enable_device(struct cpuidle_driver *drv,
>>   static void ladder_reflect(struct cpuidle_device *dev, int index)
>>   {
>>          struct ladder_device *ldev = &__get_cpu_var(ladder_devices);
>> -       if (index > 0)
>> -               ldev->last_state_idx = index;
>> +       ldev->last_state_idx = index;
>>   }
>>
>>   static struct cpuidle_governor ladder_governor = {
>> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
>> index a17515f..3907301 100644
>> --- a/drivers/cpuidle/governors/menu.c
>> +++ b/drivers/cpuidle/governors/menu.c
>> @@ -365,9 +365,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>>   static void menu_reflect(struct cpuidle_device *dev, int index)
>>   {
>>          struct menu_device *data = &__get_cpu_var(menu_devices);
>> -       data->last_state_idx = index;
>> -       if (index >= 0)
>> -               data->needs_update = 1;
>> +       data->needs_update = 1;
>
> Why is the last_state_idx not getting updated ?

Oups, right. This is missing.

Thanks for pointing this out.

By the way, I don't think a back end driver is changing the selected 
state currently and I am not sure this is desirable since we want to 
trust the state we are going (as a best effort). So if the 'enter' 
function does not change the index, that means the last_state_idx has 
not to be changed since it has been assigned in the 'select' function.



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