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

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Date:   Thu, 27 Oct 2016 20:41:27 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Paolo Valente <paolo.valente@...aro.org>,
        Christoph Hellwig <hch@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        linux-block@...r.kernel.org,
        Linux-Kernal <linux-kernel@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Hannes Reinecke <hare@...e.de>,
        Grant Likely <grant.likely@...retlab.ca>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra
 scheduler

On Thu, Oct 27, 2016 at 12:21:06PM -0600, Jens Axboe wrote:
> On 10/27/2016 12:13 PM, Ulf Hansson wrote:

> > I can imagine, that it's not always a straight forward "convert to blk
> > mq" patch for every block device driver.

> Well, I've actually done a few conversions, and it's not difficult at
> all. The grunt of the work is usually around converting to using some of
> the blk-mq features for parts of the driver that it had implemented
> privately, like timeout handling, etc.

Plus the benchmarking to verify that it works well of course, especially
initially where it'll also be a new queue infrastructure as well as the
blk-mq conversion itself.  It does feel like something that's going to
take at least a couple of kernel releases to get through.

> > > > 3)
> > > > While we work on scheduling in blkmq (at least for single queue
> > > > devices), it's of course important that we set high goals. Having BFQ
> > > > (and the other schedulers) in the legacy blk, provides a good
> > > > reference for what we could aim for.

> > > Sure, but you don't need BFQ to be included in the kernel for that.

> > Perhaps not.

> > But does that mean, you expect Paolo to maintain an up to date BFQ
> > tree for you?

> I don't expect anything. If Paolo or others want to compare with BFQ on
> the legacy IO path, then they can do that however way they want. If you
> (and others) want to have that reference point, it's up to you how to
> accomplish that.

I think there's also value in having improvements there for people who
benefit from them while queue infrastructure for blk-mq is being worked
on.  

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