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

[Jens Axboe]

On 10/26/2016 09:29 AM, Christoph Hellwig wrote:
> 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.

It's the only right way forward. blk-mq might not offer any substantial
advantages to rotating storage, but with scheduling, it won't offer a
downside either. And it'll take us towards the real goal, which is to
have just one IO path. Adding a new scheduler for the legacy IO path
makes no sense. Adding one for blk-mq and phasing out the old path is
what we need to do.

--
Jens Axboe