Re: [PATCH] ublk: optimize ublk_rq_has_data()

[Caleb Sander Mateos]

On Tue, Apr 21, 2026 at 4:51 PM Ming Lei <tom.leiming@xxxxxxxxx> wrote:
>
> On Tue, Apr 21, 2026 at 01:47:42PM -0600, Caleb Sander Mateos wrote:
> > ublk_rq_has_data() currently uses bio_has_data(), which involves 2
> > indirections and several branches. Use blk_rq_bytes() instead, which
> > performs a single indirection with no branches.
> >
> > Signed-off-by: Caleb Sander Mateos <csander@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/block/ublk_drv.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> > index ef8a0705e68b..5f9b3c3876f4 100644
> > --- a/drivers/block/ublk_drv.c
> > +++ b/drivers/block/ublk_drv.c
> > @@ -1172,11 +1172,11 @@ static inline struct ublk_queue *ublk_get_queue(struct ublk_device *dev,
> >       return dev->queues[qid];
> >  }
> >
> >  static inline bool ublk_rq_has_data(const struct request *rq)
> >  {
> > -     return bio_has_data(rq->bio);
> > +     return blk_rq_bytes(rq);
> >  }
>
> blk_rq_bytes() doesn't return the actual payload data bytes, such as,
> discard command, but bio_has_data() does.

So you're saying that on a discard, rq->__data_len is set to
bio->bi_iter.bi_size, which represents the number of bytes being
trimmed even though there's no data payload? I guess we could check
req_op(rq) here to at least avoid the bio indirection.

Thanks,
Caleb