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Date:   Mon, 15 May 2023 14:22:18 -0600
From:   Keith Busch <kbusch@kernel.org>
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH V2 2/2] blk-mq: make sure elevator callbacks aren't
 called for passthrough request
Message-ID: <ZGKUehOEnKThjFpR@kbusch-mbp>
References: <20230515144601.52811-1-ming.lei@redhat.com>
 <20230515144601.52811-3-ming.lei@redhat.com>
 <c0c4fc86-29ff-5a70-1f32-dca9af4602d5@acm.org>
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On Mon, May 15, 2023 at 08:52:38AM -0700, Bart Van Assche wrote:
> On 5/15/23 07:46, Ming Lei wrote:
> > @@ -48,7 +53,7 @@ blk_mq_sched_allow_merge(struct request_queue *q, struct request *rq,
> >   static inline void blk_mq_sched_completed_request(struct request *rq, u64 now)
> >   {
> > -	if (rq->rq_flags & RQF_ELV) {
> > +	if ((rq->rq_flags & RQF_ELV) && !blk_mq_bypass_sched(rq->cmd_flags)) {
> >   		struct elevator_queue *e = rq->q->elevator;
> >   		if (e->type->ops.completed_request)
> > @@ -58,7 +63,7 @@ static inline void blk_mq_sched_completed_request(struct request *rq, u64 now)
> >   static inline void blk_mq_sched_requeue_request(struct request *rq)
> >   {
> > -	if (rq->rq_flags & RQF_ELV) {
> > +	if ((rq->rq_flags & RQF_ELV) && !blk_mq_bypass_sched(rq->cmd_flags)) {
> >   		struct request_queue *q = rq->q;
> >   		struct elevator_queue *e = q->elevator;
> 
> Has it been considered not to set RQF_ELV for passthrough requests instead
> of making the above changes?

That sounds like a good idea. It changes more behavior than what Ming is
targeting here, but after looking through each use for RQF_ELV, I think
not having that set really is the right thing to do in all cases for
passthrough requests.