On Mon, Jan 15 2018 at 12:29pm -0500,
Jens Axboe <axboe@xxxxxxxxx> 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.
Yeap, good point.
> But more importantly, who puts the
> driver tag and the budget if we get != OK for ->queue_rq()?
__blk_mq_try_issue_directly() processes the returned value same as before
this patch. Means this patch isn't making any functional change:
If BLK_STS_RESOURCE: __blk_mq_requeue_request() is called.
__blk_mq_requeue_request() will blk_mq_put_driver_tag().
Otherwise, all other errors result in blk_mq_end_request(rq, ret);
So ignoring this patch, are you concerned that:
1) Does blk_mq_end_request() put both? Looks like blk_mq_free_request()
handles rq->tag != -1 but why not have it use __blk_mq_put_driver_tag()?
I'm not seeing where the budget is put from blk_mq_end_request()...
2) Nothing seems to be putting the budget in
__blk_mq_try_issue_directly()'s BLK_STS_RESOURCE error path? I share
your concern now (for drivers who set {get,put}_budget in mq_ops).
Should __blk_mq_requeue_request() be updated to also
blk_mq_put_dispatch_budget()?
Mike
