Re: [PATCH 0/4] blk-mq-sched: allow to use hw tag for sched

[Ming Lei <ming.lei@redhat.com>]

On Wed, Apr 19, 2017 at 06:55:30PM -0600, Jens Axboe wrote:
> On 04/19/2017 06:44 PM, Ming Lei wrote:
> > On Wed, Apr 19, 2017 at 02:17:45PM -0600, Jens Axboe wrote:
> >> On 04/15/2017 06:38 AM, Ming Lei wrote:
> >>> The 1st patch enhances BLK_MQ_F_NO_SCHED so that we can't change/
> >>> show available io schedulers on devices which don't support io
> >>> scheduler.
> >>>
> >>> The 2nd patch passes BLK_MQ_F_NO_SCHED for avoiding one regression
> >>> on mtip32xx, which is introduced by blk-mq io scheduler.
> >>
> >> I've added 1-2 for 4.11 for now, and then let's plan on getting
> >> a real fix done for 4.12.
> > 
> > The real fix has been posted out already:
> > 
> > 	http://marc.info/?t=149256196700001&r=1&w=2
> > 
> > Could you consider that for 4.12?
> 
> I didn't particularly like that approach. And we are really late
> in the 4.11 cycle, and your first two patches fit the bill for
> how we should fix it in the interim.

If we don't need to reserve tag for internal command, I am happy
to fix it in the interim. However, the mtip32xx driver has to
ask blk-mq to reserve the tag zero for internal command. Then
if we can't allow the driver to use that reserved tag, it looks
quite awkward, doesn't it?

> I'll take a closer look for 4.12, I want to get this fixed
> for real, obviously.

OK, thanks, let's discuss on solutions.

Thanks,
Ming