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 08:05:11 -0700
From:   Bart Van Assche <bart.vanassche@...disk.com>
To:     Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>
CC:     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>, <arnd@...db.de>,
        <bart.vanassche@...disk.com>, <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 10/26/2016 04:34 AM, Jan Kara wrote:
> On Wed 26-10-16 03:19:03, Christoph Hellwig wrote:
>> Just as last time:
>>
>> big NAK for introducing giant new infrastructure like a new I/O scheduler
>> for the legacy request structure.
>>
>> Please direct your engergy towards blk-mq instead.
>
> Christoph, we will probably talk about this next week but IMO rotating
> disks and SATA based SSDs are going to stay with us for another 15 years,
> likely more. For them blk-mq is no win, relatively complex IO scheduling
> like CFQ or BFQ does is a big win for them in some cases. So I think IO
> scheduling (and thus place for something like BFQ) is going to stay with us
> for quite a long time still. So are we going to add hooks in blk-mq to
> support full-blown IO scheduling at least for single queue devices? Or how
> else do we want to support that HW?

Hello Jan,

Having two versions (one for non-blk-mq, one for blk-mq) of every I/O 
scheduler would be a maintenance nightmare. Has anyone already analyzed 
whether it would be possible to come up with an API for I/O schedulers 
that makes it possible to use the same I/O scheduler for both blk-mq and 
the traditional block layer?

Bart.