On Tue, Jan 16, 2018 at 9:40 AM, Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> On Mon, Jan 15, 2018 at 10:29:46AM -0700, Jens Axboe wrote:
>> On 1/15/18 9:58 AM, Ming Lei wrote:
>> > No functional change, just to clean up code a bit, so that the following
>> > change of using direct issue for blk_mq_request_bypass_insert() which is
>> > needed by DM can be easier to do.
>> >
>> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
>> > ---
>> > block/blk-mq.c | 39 +++++++++++++++++++++++++++------------
>> > 1 file changed, 27 insertions(+), 12 deletions(-)
>> >
>> > diff --git a/block/blk-mq.c b/block/blk-mq.c
>> > index edb1291a42c5..bf8d6651f40e 100644
>> > --- a/block/blk-mq.c
>> > +++ b/block/blk-mq.c
>> > @@ -1696,15 +1696,37 @@ static blk_qc_t request_to_qc_t(struct blk_mq_hw_ctx *hctx, struct request *rq)
>> > return blk_tag_to_qc_t(rq->internal_tag, hctx->queue_num, true);
>> > }
>> >
>> > -static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>> > - struct request *rq,
>> > - blk_qc_t *cookie)
>> > +static blk_status_t __blk_mq_issue_req(struct blk_mq_hw_ctx *hctx,
>> > + struct request *rq,
>> > + blk_qc_t *new_cookie)
>> > {
>> > + blk_status_t ret;
>> > struct request_queue *q = rq->q;
>> > struct blk_mq_queue_data bd = {
>> > .rq = rq,
>> > .last = true,
>> > };
>> > +
>> > + if (!blk_mq_get_driver_tag(rq, NULL, false))
>> > + return BLK_STS_AGAIN;
>> > +
>> > + if (!blk_mq_get_dispatch_budget(hctx)) {
>> > + blk_mq_put_driver_tag(rq);
>> > + return BLK_STS_AGAIN;
>> > + }
>> > +
>> > + *new_cookie = request_to_qc_t(hctx, rq);
>> > +
>> > + ret = q->mq_ops->queue_rq(hctx, &bd);
>> > +
>> > + return ret;
>>
>> return q->mq_ops->queue_rq(hctx, &bd);
>>
>> and kill 'ret', it's not used. But more importantly, who puts the
>
> OK.
>
>> driver tag and the budget if we get != OK for ->queue_rq()?
>
> For the budget, the current protocol is that driver is responsible for the
> release once .queue_rq is called, see scsi_mq_queue_rq() and comment in
> blk_mq_do_dispatch_sched().
>
> For driver tag, it is released in blk_mq_free_request(), which is done
> in failure handling of != OK.
Actually the driver tag should be released here when .queue_rq()
returns !OK, and this patch does follow the current logic:
- call __blk_mq_requeue_request() to release tag and make it ready
for requeue if STS_RESOURCE is returned.
- For other !OK cases, let driver free the request.
--
Ming Lei
