Re: [PATCH 04/14] bfq: use bfq_bic_lookup in bfq_limit_depth

[Jan Kara <jack@suse.cz>]

On Tue 30-11-21 07:39:55, Christoph Hellwig wrote:
> On Mon, Nov 29, 2021 at 05:09:25PM +0100, Jan Kara wrote:
> > On Fri 26-11-21 12:58:07, Christoph Hellwig wrote:
> > > No need to create a new I/O context if there is none present yet in
> > > ->limit_depth.
> > > 
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > ---
> > >  block/bfq-iosched.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> > > index c990c6409c119..ecc2e57e68630 100644
> > > --- a/block/bfq-iosched.c
> > > +++ b/block/bfq-iosched.c
> > > @@ -663,7 +663,7 @@ static bool bfqq_request_over_limit(struct bfq_queue *bfqq, int limit)
> > >  static void bfq_limit_depth(unsigned int op, struct blk_mq_alloc_data *data)
> > >  {
> > >  	struct bfq_data *bfqd = data->q->elevator->elevator_data;
> > > -	struct bfq_io_cq *bic = icq_to_bic(blk_mq_sched_get_icq(data->q));
> > > +	struct bfq_io_cq *bic = bfq_bic_lookup(data->q);
> > 
> > Maybe I'm missing something but bfq_limit_depth() needs to know to which
> > BFQ queue (and consequently blkcg) this IO is going to be added. And to be
> > able to lookup this queue we are using IO context. So AFAICT we need the
> > IO context allocated already in bfq_limit_depth()?
> 
> But by allocating it you won't now anything, as it will still be empty.

You're right, we'll create only IO context and corresponding bfq_io_cq but
we won't actually create bfqq in bfq_limit_depth() anyway and without that
bfq_limit_depth() isn't going to do more. So your patch indeed does not
change anything in that regard.

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR