linux-kernel - Re: [RFC PATCH 3/5] cfq-iosched: reimplement priorities using different service trees

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Date:	Tue, 20 Oct 2009 12:43:20 +0200
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [RFC PATCH 3/5] cfq-iosched: reimplement priorities using 
	different service trees

On Tue, Oct 20, 2009 at 2:58 AM, Jens Axboe <jens.axboe@...cle.com> wrote:
> On Mon, Oct 19 2009, Corrado Zoccolo wrote:
>> We use different service trees for different priority classes.
>> This allows a simplification in the service tree insertion code, that no
>> longer has to consider priority while walking the tree.
>
>> +enum wl_prio_t {
>> +     IDLE_WL = -1,
>> +     BE_WL = 0,
>> +     RT_WL = 1
>> +};
>
> WL?
It stands for "workload". When defining all-caps constants, one has to
avoid possible clashes adding pre/suf-fixes.
Any suggestion for better naming?
>
>> +static struct cfq_rb_root *service_tree_for(enum wl_prio_t prio,
>> +                                     struct cfq_data *cfqd)
>> +{
>> +     return prio == IDLE_WL ? &cfqd->service_tree_idle :
>> +             &cfqd->service_trees[prio];
>> +}
>
> Don't do it...
>
> static struct cfq_rb_root *service_tree_for(enum wl_prio_t prio,
>                                        struct cfq_data *cfqd)
> {
>        if (prio == IDLE_WL)
>                return &cfqd->service_tree_idle;
>
>        return &cfqd->service_trees[prio];
> }
>
> much cleaner. There are more of these in this patch.
I don't see much difference: my brain just translates the former in
the latter, and the former takes up less screen space.
But you are the maintainer, so I'll write it as you want.

> Otherwise it looks sane, and I agree that making the insert cleaner here
> is a good bonus.

Thanks
Corrado
>
> --
> Jens Axboe
>
>
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