linux-kernel - Re: [PATCH 08/17] ioprio: Add a macro named NICE_TO

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Date:	Wed, 12 Mar 2014 17:41:58 +0800
From:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
To:	Dongsheng Yang <yangds.fnst@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	joe@...ches.com, mingo@...nel.org, tglx@...utronix.de,
	heiko.carstens@...ibm.com
Subject: Re: [PATCH 08/17] ioprio: Add a macro named NICE_TO_IOPRIO.

On 03/11/2014 06:09 PM, 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)
> +

Hi Peter,
     As you asked, why I added this macro in ioprio.h? And why it is better?

     IMO, there is a policy to convert a nice value to io priority, that 
divide the nice
range into 8 parts by 5. I think this is a common requirement for lots 
of io subsystem.
So I implement this policy with NICE_TO_IOPRIO.

     About function task_nice_iopiro(), it is to get the iopriority of a 
task. It should get the
nice value at first and then use the NICE_TO_IOPRIO to convert it to 
ioprio in the policy.

When our policy changed, we need only update the center controller, 
NICE_TO_IOPRIO.
Keep the others work well.

This is my point about this patch. I wish it explained better. Thanx.
> +/*
>    * 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));
>   }
>   
>   /*

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