linux-kernel - Re: [PATCH 02/18] io-controller: Common flat fair queuing code in elevaotor layer

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Message-ID: <4A164978.1020604@cn.fujitsu.com>
Date:	Fri, 22 May 2009 14:43:04 +0800
From:	Gui Jianfeng <guijianfeng@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
	jens.axboe@...cle.com, ryov@...inux.co.jp, fernando@....ntt.co.jp,
	s-uchida@...jp.nec.com, taka@...inux.co.jp, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, righi.andrea@...il.com,
	agk@...hat.com, dm-devel@...hat.com, snitzer@...hat.com,
	m-ikeda@...jp.nec.com, akpm@...ux-foundation.org
Subject: Re: [PATCH 02/18] io-controller: Common flat fair queuing code in
 elevaotor layer

Vivek Goyal wrote:
...
> +/* A request got completed from io_queue. Do the accounting. */
> +void elv_ioq_completed_request(struct request_queue *q, struct request *rq)
> +{
> +	const int sync = rq_is_sync(rq);
> +	struct io_queue *ioq = rq->ioq;
> +	struct elv_fq_data *efqd = &q->elevator->efqd;
> +
> +	if (!elv_iosched_fair_queuing_enabled(q->elevator))
> +		return;
> +
> +	elv_log_ioq(efqd, ioq, "complete");
> +
> +	elv_update_hw_tag(efqd);
> +
> +	WARN_ON(!efqd->rq_in_driver);
> +	WARN_ON(!ioq->dispatched);
> +	efqd->rq_in_driver--;
> +	ioq->dispatched--;
> +
> +	if (sync)
> +		ioq->last_end_request = jiffies;
> +
> +	/*
> +	 * If this is the active queue, check if it needs to be expired,
> +	 * or if we want to idle in case it has no pending requests.
> +	 */
> +
> +	if (elv_active_ioq(q->elevator) == ioq) {
> +		if (elv_ioq_slice_new(ioq)) {
> +			elv_ioq_set_prio_slice(q, ioq);

  Hi Vivek,

  Would you explain a bit why slice_end should be set when first request completes.
  Why not set it just when an ioq gets active?
  
  Thanks.
  Gui Jianfeng


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