linux-kernel - Re: [PATCH 02/20] io-controller: Common flat fair queuing code in elevaotor layer

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Date:	Mon, 22 Jun 2009 22:20:24 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.com, nauman@...gle.com, dpshah@...gle.com,
	lizf@...fujitsu.com, mikew@...gle.com, fchecconi@...il.com,
	paolo.valente@...more.it, ryov@...inux.co.jp,
	fernando@....ntt.co.jp, s-uchida@...jp.nec.com, taka@...inux.co.jp,
	guijianfeng@...fujitsu.com, dhaval@...ux.vnet.ibm.com,
	righi.andrea@...il.com, m-ikeda@...jp.nec.com, jbaron@...hat.com,
	agk@...hat.com, snitzer@...hat.com, akpm@...ux-foundation.org,
	peterz@...radead.org
Subject: Re: [PATCH 02/20] io-controller: Common flat fair queuing code in elevaotor layer

Vivek Goyal <vgoyal@...hat.com> writes:

> On Mon, Jun 22, 2009 at 02:16:12PM +0530, Balbir Singh wrote:
>> > +	ioq->pid = current->pid;
>> 
>> Is pid used for cgroup association later? I don't see why we save the
>> pid otherwise? If yes, why not store the cgroup of the current->pid?
>> 
>
> This is just for logging purposes (blktrace), useful for CFQ where every task
> context sets up one queue and this number becomes the identifier for the queue.
> Look at elv_log_ioq(), which uses ioq->pid.

Well, that's not 100% accurate as tasks can share I/O contexts.
However, the 1:1 mapping does hold true most of the time.

> [..]
>> > + * coop tells that io scheduler selected a queue for us and we did not
>> 
>> coop?
>
> coop refers to "cooperating". I guess "coop" is not descriptive. I will
> change the name to "cooperating" and also put more description for
> clarity.

I think just more description is fine.  I'm not sure you need to spell
out cooperating (that will make for some long lines!).

>> > +	struct io_queue *async_idle_queue;
>> > +
>> > +	/*
>> > +	 * Used to track any pending rt requests so we can pre-empt current
>> > +	 * non-RT cfqq in service when this value is non-zero.
>> > +	 */
>> > +	unsigned int busy_rt_queues;
>> > +};
>> > +
>> > +struct elv_fq_data {
>> 
>> What does fq stand for?
>
> Fair queuing. Any suggestions to make it better?

I think you could just put it in the comment.

Cheers,
Jeff
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