linux-kernel - Re: [PATCH 02/24] io-controller: Core of the elevator fair queuing

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Message-ID: <20090819184142.GD4391@redhat.com>
Date:	Wed, 19 Aug 2009 14:41:42 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Jerome Marchand <jmarchan@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, ryov@...inux.co.jp,
	balbir@...ux.vnet.ibm.com, righi.andrea@...il.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
	fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp,
	guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, m-ikeda@...jp.nec.com, agk@...hat.com,
	akpm@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH 02/24] io-controller: Core of the elevator fair queuing

On Wed, Aug 19, 2009 at 06:01:34PM +0200, Jerome Marchand wrote:
> Hi Vivek,
> 
> Vivek Goyal wrote:
> > o This is core of the io scheduler implemented at elevator layer. This is a mix
> >   of cpu CFS scheduler and CFQ IO scheduler. Some of the bits from CFS have
> >   to be derived so that we can support hierarchical scheduling. Without
> >   cgroups or with-in group, we should essentially get same behavior as CFQ.
> > 
> > o This patch only shows non-hierarchical bits. Hierarhical code comes in later
> >   patches.
> > 
> > o This code is the building base of introducing fair queuing logic in common
> >   elevator layer so that it can be used by all the four IO schedulers.
> 
> > +static void enqueue_io_entity(struct io_entity *entity)
> > +{
> > +	struct io_service_tree *st = entity->st;
> > +	struct io_sched_data *sd = io_entity_sched_data(entity);
> > +
> > +	/* In case task ioprio class changed while entity was off tree */
> > +	io_entity_update_prio(entity);
> > +	st->nr_active++;
> > +	sd->nr_active++;
> > +	entity->on_st = 1;
> > +	place_entity(st, entity, 0);
> > +	__enqueue_io_entity(st, entity);
> > +}
> 
> > +static void put_prev_io_entity(struct io_entity *entity)
> > +{
> > +	struct io_service_tree *st = entity->st;
> > +	struct io_sched_data *sd = io_entity_sched_data(entity);
> > +
> > +	st->active_entity = NULL;
> > +	sd->active_entity = NULL;
> > +
> > +	if (unlikely(entity->ioprio_changed)) {
> > +		dequeue_io_entity(entity);
> > +		io_entity_update_prio(entity);
> 
> That call to io_entity_update_prio() looks redundant with the one in
> enqueue_io_entity().
> 

thanks Jerome. Yes it does look like a redundant call. Will get rid of it
in next posting.

Vivek

> > +		enqueue_io_entity(entity);
> > +	} else
> > +		__enqueue_io_entity(st, entity);
> > +}
> 
> Jerome
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