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

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Date:	Fri, 4 Mar 2016 13:10:31 -0500
From:	"Austin S. Hemmelgarn" <ahferroin7@...il.com>
To:	Christoph Hellwig <hch@...radead.org>,
	Linus Walleij <linus.walleij@...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>,
	Ulf Hansson <ulf.hansson@...aro.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH RFC 09/22] block, cfq: replace CFQ with the BFQ-v0 I/O
 scheduler

On 2016-03-04 12:39, Christoph Hellwig wrote:
> On Sat, Mar 05, 2016 at 12:29:39AM +0700, Linus Walleij wrote:
>> Hi Tejun,
>>
>> I'm doing a summary of this discussion as a part of presenting
>> Linaro's involvement in Paolo's work. So I try to understand things.
>
> 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?
>
1. This all started long before blk-mq hit mainline.
2. There's still a decent amount of block drivers that don't support 
blk-mq.  Last time I looked (around the time 4.4 came out), I saw the 
following that either obviously don't support it, or are ambiguous as to 
whether they support it or not.  Here's a list of just the ones I know 
are being used on existing systems running relatively recent kernel 
versions, not including any of the MTD stuff:
     * fd
     * MD
     * bcache
     * mmcblk
     * nbd
     * dasd
     * drbd
     * rbd
     * aoe
     * xvd (I know there were patches for this floating around, but I 
never saw if they got merged or not)