[dm-devel] dm mpath: switch IO scheduler of underlying paths to "none" [was: Re: BFQ + dm-mpath]
Mike Snitzer
snitzer at redhat.com
Fri Sep 8 19:58:05 UTC 2017
On Fri, Sep 08 2017 at 1:07pm -0400,
Mike Snitzer <snitzer at redhat.com> wrote:
> On Fri, Sep 08 2017 at 12:48pm -0400,
> Jens Axboe <axboe at kernel.dk> wrote:
>
> > > Please see the following untested patch. All
> > > testing/review/comments/acks appreciated.
> > >
> > > I elected to use elevator_change() rather than fiddle with adding a new
> > > blk-mq elevator hook (e.g. ->request_prepared) to verify that each
> > > blk-mq elevator enabled request did in fact get prepared.
> > >
> > > Bart, please test this patch and reply with your review/feedback.
> > >
> > > Jens, if you're OK with this solution please reply with your Ack and
> > > I'll send it to Linus along with the rest of the handful of DM changes I
> > > have for 4.14.
> >
> > I am not - we used to have this elevator change functionality from
> > inside the kernel, and finally got rid of it when certain drivers killed
> > it. I don't want to be bringing it back.
>
> Fine.
BTW, while I conceded "Fine": I think your justification for not
reintroducing elevator_change() lacks substance. What is inherently
problematic about elevator_change()?
Having an elevator attached to a DM multipath device's underlying path's
request_queue just asks for trouble (especially given the blk-mq
elevator interface).
Please own this issue as a regression and help me arrive at a timely way
forward.
Thanks,
Mike
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