linux-kernel - Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler

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Date:   Wed, 26 Oct 2016 08:29:55 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Bart Van Assche <bart.vanassche@...disk.com>,
        Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
        Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ulf.hansson@...aro.org, linus.walleij@...aro.org,
        broonie@...nel.org, hare@...e.de, grant.likely@...retlab.ca,
        James.Bottomley@...senpartnership.com
Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra
 scheduler

On Wed, Oct 26, 2016 at 05:13:07PM +0200, Arnd Bergmann wrote:
> The question to ask first is whether to actually have pluggable
> schedulers on blk-mq at all, or just have one that is meant to
> do the right thing in every case (and possibly can be bypassed
> completely).

That would be my preference.  Have a BFQ-variant for blk-mq as an
option (default to off unless opted in by the driver or user), and
not other scheduler for blk-mq.  Don't bother with bfq for non
blk-mq.  It's not like there is any advantage in the legacy-request
device even for slow devices, except for the option of having I/O
scheduling.