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

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Message-ID: <CACRpkdZugGOPkYaKnQjY-SJ5-+OCiv_mmWvd3=eM=_ACd+UQQA@mail.gmail.com>
Date:	Sat, 5 Mar 2016 19:18:30 +0700
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Christoph Hellwig <hch@...radead.org>,
	Ulf Hansson <ulf.hansson@...aro.org>
Cc:	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 5, 2016 at 12:39 AM, Christoph Hellwig <hch@...radead.org> wrote:

> Btw, can someone explain why you guys waste so much time hacking and
> arguing about a legacy codebase (old request code and I/O schedulers)
> that everyone would really like to see disappear.  Why don't you
> spend your time on blk-mq where you have an entirely clean slate
> for scheduling?

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.

So: large userbase in all things handheld.

Yours,
Linus Walleij