On Wed, Nov 17, 2021 at 08:43:02AM -0700, Jens Axboe wrote:
> On 11/17/21 1:20 AM, Ming Lei wrote:
> > On Tue, Nov 16, 2021 at 08:38:04PM -0700, Jens Axboe wrote:
> >> If we have a list of requests in our plug list, send it to the driver in
> >> one go, if possible. The driver must set mq_ops->queue_rqs() to support
> >> this, if not the usual one-by-one path is used.
> >>
> >> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
> >> ---
> >> block/blk-mq.c | 17 +++++++++++++++++
> >> include/linux/blk-mq.h | 8 ++++++++
> >> 2 files changed, 25 insertions(+)
> >>
> >> diff --git a/block/blk-mq.c b/block/blk-mq.c
> >> index 9b4e79e2ac1e..005715206b16 100644
> >> --- a/block/blk-mq.c
> >> +++ b/block/blk-mq.c
> >> @@ -2208,6 +2208,19 @@ static void blk_mq_plug_issue_direct(struct blk_plug *plug, bool from_schedule)
> >> int queued = 0;
> >> int errors = 0;
> >>
> >> + /*
> >> + * Peek first request and see if we have a ->queue_rqs() hook. If we
> >> + * do, we can dispatch the whole plug list in one go. We already know
> >> + * at this point that all requests belong to the same queue, caller
> >> + * must ensure that's the case.
> >> + */
> >> + rq = rq_list_peek(&plug->mq_list);
> >> + if (rq->q->mq_ops->queue_rqs) {
> >> + rq->q->mq_ops->queue_rqs(&plug->mq_list);
> >> + if (rq_list_empty(plug->mq_list))
> >> + return;
> >> + }
> >> +
> >
> > Then BLK_MQ_F_TAG_QUEUE_SHARED isn't handled as before for multiple NVMe
> > NS.
>
> Can you expand? If we have multiple namespaces in the plug list, we have
> multiple queues. There's no direct issue of the list if that's the case.
> Or maybe I'm missing what you mean here?
If the plug list only has requests for one namespace, I think Ming is
referring to the special accounting for BLK_MQ_F_TAG_QUEUE_SHARED in
__blk_mq_get_driver_tag() that normally gets called before dispatching
to the driver, but isn't getting called when using .queue_rqs().
