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

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Date:	Tue, 20 Oct 2009 02:58:14 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Corrado Zoccolo <czoccolo@...il.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 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?

> +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.

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

-- 
Jens Axboe

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