Re: [PATCH] bfq: backport: update internal depth state when queue depth changes

[Sasha Levin]

On Fri, May 10, 2019 at 10:56:32AM -0700, Eric Wheeler wrote:
> From: Jens Axboe <axboe@xxxxxxxxx>
>
> commit 77f1e0a52d26242b6c2dba019f6ebebfb9ff701e upstream
>
> A previous commit moved the shallow depth and BFQ depth map calculations
> to be done at init time, moving it outside of the hotter IO path. This
> potentially causes hangs if the users changes the depth of the scheduler
> map, by writing to the 'nr_requests' sysfs file for that device.
>
> Add a blk-mq-sched hook that allows blk-mq to inform the scheduler if
> the depth changes, so that the scheduler can update its internal state.
>
> Signed-off-by: Eric Wheeler <bfq@xxxxxxxxxxxxxxxxxx>
> Tested-by: Kai Krakow <kai@xxxxxxxxxxx>
> Reported-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
> Fixes: f0635b8a416e ("bfq: calculate shallow depths at init time")
> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx

I wasn't clear on what was backported here, so I've queued the upstream
version on 4.19 and 4.14, it doesn't seem to be relevant to older
branches.

--
Thanks,
Sasha