linux-kernel - Re: [PATCH 07/16] ioprio: Add a macro named NICE_TO

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Date:	Tue, 11 Mar 2014 17:34:20 +0800
From:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	linux-kernel@...r.kernel.org, joe@...ches.com, mingo@...nel.org,
	tglx@...utronix.de, heiko.carstens@...ibm.com,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 07/16] ioprio: Add a macro named NICE_TO_IOPRIO.

On 03/11/2014 05:28 PM, Peter Zijlstra wrote:
> On Tue, Mar 11, 2014 at 05:20:28PM +0800, Dongsheng Yang wrote:
>> As the task nice value is in [-20, 19] and the io priority is in [0, 7],
>> and the convert method from niceval to ioprio is implemented with an
>> opened code in task_nice_ioprio().
>>
>> This patch move the implementation to a macro NICE_TO_IOPRIO, making
>> it more readable and modular.
>>
>> Signed-off-by: Dongsheng Yang <yangds.fnst@...fujitsu.com>
>> ---
>>   include/linux/ioprio.h | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
>> index beb9ce1..c0faa0b 100644
>> --- a/include/linux/ioprio.h
>> +++ b/include/linux/ioprio.h
>> @@ -18,6 +18,11 @@
>>   #define ioprio_valid(mask)	(IOPRIO_PRIO_CLASS((mask)) != IOPRIO_CLASS_NONE)
>>   
>>   /*
>> + * Convert the nice value [19,-20] to io priority value [0,7].
>> + */
>> +#define NICE_TO_IOPRIO(nice)	(nice_to_rlimit(nice) / 5)
>> +
>> +/*
>>    * These are the io priority groups as implemented by CFQ. RT is the realtime
>>    * class, it always gets premium service. BE is the best-effort scheduling
>>    * class, the default for any process. IDLE is the idle scheduling class, it
>> @@ -52,7 +57,7 @@ enum {
>>    */
>>   static inline int task_nice_ioprio(struct task_struct *task)
>>   {
>> -	return (task_nice(task) + 20) / 5;
>> +	return NICE_TO_IOPRIO(task_nice(task));
>>   }
> How exactly is adding a macro and code complexity making this code
> better?

About this patch, I think convert a nice value in [-20, 19] to ioprio in 
[0, 7]
is a common requirement. So I add a macro NICE_TO_IOPRIO to achieve it.

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