linux-kernel - Re: [PATCH V2 1/2] sched: idle: Encapsulate the code to compile it out

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Date:	Fri, 02 May 2014 15:29:45 +0200
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
CC:	peterz@...radead.org, mingo@...e.hu, amit.kucheria@...aro.org,
	linaro-kernel@...ts.linaro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: Re: [PATCH V2 1/2] sched: idle: Encapsulate the code to compile it
 out

On 05/02/2014 02:09 PM, Rafael J. Wysocki wrote:
> On Friday, May 02, 2014 10:59:11 AM Daniel Lezcano wrote:
>> On 05/01/2014 12:56 AM, Rafael J. Wysocki wrote:
>>> On Thursday, May 01, 2014 12:47:25 AM Rafael J. Wysocki wrote:
>>>> On Wednesday, April 30, 2014 02:01:02 PM Daniel Lezcano wrote:
>>>>> Encapsulate the large portion of cpuidle_idle_call inside another
>>>>> function so when CONFIG_CPU_IDLE=n, the code will be compiled out.
>>>>> Also that is benefitial for the clarity of the code as it removes
>>>>> a nested indentation level.
>>>>>
>>>>> Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
>>>>
>>>> Well, this conflicts with
>>>>
>>>> https://patchwork.kernel.org/patch/4071541/
>>>>
>>>> which you haven't commented on and I still want cpuidle_select() to be able to
>>>> return negative values because of
>>>>
>>>> https://patchwork.kernel.org/patch/4089631/
>>>>
>>>> (and I have one more patch on top of these two that requires this).
>>>
>>> Moreover (along the lines of Nico said) after https://patchwork.kernel.org/patch/4071541/
>>> we actually don't need the #ifdef CONFIG_CPU_IDLE in your patch, because cpuidle_select()
>>> for CONFIG_CPU_IDLE unset is a static inline returning a negative number and the compiler
>>> should optimize out the blocks that depend on it being non-negative.
>>
>> Thanks for the head up.
>>
>> Actually that was to solve a compilation issue with the next patch when
>> adding the cpuidle state in the struct rq.
>>
>> When the option CPU_IDLE is not set, the code assinging the cpu idle
>> state in the rq is still there while in the struct rq the field is
>> compiled out with the ifdef macro. If I rely on the compiler
>> optimization, the compilation error will happen.
>
> I see.
>
> If you don't put the new idle_state field in struct_rq under the #ifdef,
> you won't need to worry about the build problem.
>
> Alternatively, you can define
>
> #ifdef CONFIG_CPU_IDLE
> static inline void rq_set_idle_state(struct rq *rq, struct cpuidle_state *state)
> {
> 	rq->idle_state = state;
> }
> #else
> static inline void rq_set_idle_state(struct rq *rq, struct cpuidle_state *state) {}
> #endif
>
> and use rq_set_idle_state() to set that field.

Thanks, I will look at one or another solution.




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