Re: [PATCH] blk-mq: don't queue passthrough request into scheduler

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

On Fri, May 12, 2023 at 09:08:54AM -0600, Jens Axboe wrote:
> On 5/12/23 9:03?AM, Ming Lei wrote:
> > Passthrough(pt) request shouldn't be queued to scheduler, especially some
> > schedulers(such as bfq) supposes that req->bio is always available and
> > blk-cgroup can be retrieved via bio.
> > 
> > Sometimes pt request could be part of error handling, so it is better to always
> > queue it into hctx->dispatch directly.
> > 
> > Fix this issue by queuing pt request from plug list to hctx->dispatch
> > directly.
> 
> Why not just add the check to the BFQ insertion? That would be a lot
> more trivial and would not be poluting the core with this stuff.

pt request is supposed to be issued to device directly, and we never
queue it to scheduler before 1c2d2fff6dc0 ("block: wire-up support for
passthrough plugging").

some pt request might be part of error handling, and adding it to
scheduler could cause io hang.


Thanks,
Ming