linux-kernel - Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O scheduler

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Date:	Fri, 11 Mar 2016 03:17:14 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Tejun Heo <tj@...nel.org>,
	Paolo Valente <paolo.valente@...aro.org>,
	Jens Axboe <axboe@...nel.dk>,
	Fabio Checconi <fchecconi@...il.com>,
	Arianna Avanzini <avanzini.arianna@...il.com>,
	linux-block@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O
 scheduler

On Sat, Mar 05, 2016 at 07:18:30PM +0700, Linus Walleij wrote:
> Depends on what time horizon and target I'd say. Paolo was in contact with
> the MMC/SD subsystem maintainer Ulf Hansson. (e)MMC/SD are both
> synchronous command-response-based protocols, and as of today
> single-channel. So everone's smartphone and tablet etc are today
> single-channel. I don't know if there is even a protocol change coming
> to augment this, the only duct-tapeish solution I've heard about is
> command queueing which is basically a kind of pipelining of requests.

We use blkj-mq for single queue devices as well, in fact most consumers
are single queue.  MMC is a prime candidate that hould move over soon.