On Tue, Jun 30, 2020 at 08:26:11AM +0200, Hannes Reinecke wrote:
> On 6/30/20 4:23 AM, Ming Lei wrote:
> > Move blk_mq_tag_busy(), .nr_active update and request assignment into
> > blk_mq_get_driver_tag(), all are good to do during getting driver tag.
> >
> > Meantime blk-flush related code is simplified and flush request needn't
> > to update the request table manually any more.
> >
> > Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> > block/blk-flush.c | 13 ++++---------
> > block/blk-mq-tag.h | 12 ------------
> > block/blk-mq.c | 33 +++++++++++++--------------------
> > block/blk.h | 5 -----
> > 4 files changed, 17 insertions(+), 46 deletions(-)
> >
> > diff --git a/block/blk-flush.c b/block/blk-flush.c
> > index 21108a550fbf..3b0c5cfe922a 100644
> > --- a/block/blk-flush.c
> > +++ b/block/blk-flush.c
> > @@ -236,12 +236,10 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
> > error = fq->rq_status;
> > hctx = flush_rq->mq_hctx;
> > - if (!q->elevator) {
> > - blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
> > + if (!q->elevator)
> > flush_rq->tag = -1;
> > - } else {
> > + else
> > flush_rq->internal_tag = -1;
> > - }
> > running = &fq->flush_queue[fq->flush_running_idx];
> > BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
> > @@ -315,13 +313,10 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
> > flush_rq->mq_ctx = first_rq->mq_ctx;
> > flush_rq->mq_hctx = first_rq->mq_hctx;
> > - if (!q->elevator) {
> > - fq->orig_rq = first_rq;
> > + if (!q->elevator)
> > flush_rq->tag = first_rq->tag;
> > - blk_mq_tag_set_rq(flush_rq->mq_hctx, first_rq->tag, flush_rq);
> > - } else {
> > + else
> > flush_rq->internal_tag = first_rq->internal_tag;
> > - }
> > flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
> > flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
> > diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
> > index 3945c7f5b944..b1acac518c4e 100644
> > --- a/block/blk-mq-tag.h
> > +++ b/block/blk-mq-tag.h
> > @@ -101,18 +101,6 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
> > return atomic_read(&hctx->nr_active) < depth;
> > }
> > -/*
> > - * This helper should only be used for flush request to share tag
> > - * with the request cloned from, and both the two requests can't be
> > - * in flight at the same time. The caller has to make sure the tag
> > - * can't be freed.
> > - */
> > -static inline void blk_mq_tag_set_rq(struct blk_mq_hw_ctx *hctx,
> > - unsigned int tag, struct request *rq)
> > -{
> > - hctx->tags->rqs[tag] = rq;
> > -}
> > -
> > static inline bool blk_mq_tag_is_reserved(struct blk_mq_tags *tags,
> > unsigned int tag)
> > {
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index cabeeeb3d56c..44b101757d33 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -277,26 +277,20 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
> > {
> > struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
> > struct request *rq = tags->static_rqs[tag];
> > - req_flags_t rq_flags = 0;
> > if (data->flags & BLK_MQ_REQ_INTERNAL) {
> > rq->tag = BLK_MQ_NO_TAG;
> > rq->internal_tag = tag;
> > } else {
> > - if (data->hctx->flags & BLK_MQ_F_TAG_SHARED) {
> > - rq_flags = RQF_MQ_INFLIGHT;
> > - atomic_inc(&data->hctx->nr_active);
> > - }
> > rq->tag = tag;
> > rq->internal_tag = BLK_MQ_NO_TAG;
> > - data->hctx->tags->rqs[rq->tag] = rq;
> > }
> > /* csd/requeue_work/fifo_time is initialized before use */
> > rq->q = data->q;
> > rq->mq_ctx = data->ctx;
> > rq->mq_hctx = data->hctx;
> > - rq->rq_flags = rq_flags;
> > + rq->rq_flags = 0;
> > rq->cmd_flags = data->cmd_flags;
> > if (data->flags & BLK_MQ_REQ_PREEMPT)
> > rq->rq_flags |= RQF_PREEMPT;
> > @@ -380,8 +374,6 @@ static struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data)
> > retry:
> > data->ctx = blk_mq_get_ctx(q);
> > data->hctx = blk_mq_map_queue(q, data->cmd_flags, data->ctx);
> > - if (!(data->flags & BLK_MQ_REQ_INTERNAL))
> > - blk_mq_tag_busy(data->hctx);
> > /*
> > * Waiting allocations only fail because of an inactive hctx. In that
> > @@ -478,8 +470,6 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
> > if (q->elevator)
> > data.flags |= BLK_MQ_REQ_INTERNAL;
> > - else
> > - blk_mq_tag_busy(data.hctx);
> > ret = -EWOULDBLOCK;
> > tag = blk_mq_get_tag(&data);
> > @@ -1131,7 +1121,6 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
> > {
> > struct sbitmap_queue *bt = &rq->mq_hctx->tags->bitmap_tags;
> > unsigned int tag_offset = rq->mq_hctx->tags->nr_reserved_tags;
> > - bool shared = blk_mq_tag_busy(rq->mq_hctx);
> > int tag;
> > if (blk_mq_tag_is_reserved(rq->mq_hctx->sched_tags, rq->internal_tag)) {
> > @@ -1146,19 +1135,23 @@ static bool __blk_mq_get_driver_tag(struct request *rq)
> > return false;
> > rq->tag = tag + tag_offset;
> > - if (shared) {
> > - rq->rq_flags |= RQF_MQ_INFLIGHT;
> > - atomic_inc(&rq->mq_hctx->nr_active);
> > - }
> > - rq->mq_hctx->tags->rqs[rq->tag] = rq;
> > return true;
> > }
> > static bool blk_mq_get_driver_tag(struct request *rq)
> > {
> > - if (rq->tag != BLK_MQ_NO_TAG)
> > - return true;
> > - return __blk_mq_get_driver_tag(rq);
> > + struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
> > + bool shared = blk_mq_tag_busy(rq->mq_hctx);
> > +
> > + if (rq->tag == BLK_MQ_NO_TAG && !__blk_mq_get_driver_tag(rq))
> > + return false;
> > +
> > + if (shared) {
> > + rq->rq_flags |= RQF_MQ_INFLIGHT;
> > + atomic_inc(&hctx->nr_active);
> > + }
> > + hctx->tags->rqs[rq->tag] = rq;
> > + return true;
> > }
> > static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
> > diff --git a/block/blk.h b/block/blk.h
> > index 3a120a070dac..459790f9783d 100644
> > --- a/block/blk.h
> > +++ b/block/blk.h
> > @@ -25,11 +25,6 @@ struct blk_flush_queue {
> > struct list_head flush_data_in_flight;
> > struct request *flush_rq;
> > - /*
> > - * flush_rq shares tag with this rq, both can't be active
> > - * at the same time
> > - */
> > - struct request *orig_rq;
> > struct lock_class_key key;
> > spinlock_t mq_flush_lock;
> > };
> >
> Can you give some more explanation why it's safe to move blk_mq_tag_busy()
> into blk_mq_get_driver_tag(), seeing that it was called before
> blk_mq_get_tag() initially?
In theory, it should be done before blk_mq_get_tag() in case of none
because hctx_may_queue() will use this info for deciding if one driver
tag can be allocated for this lun/ns for the sake of fairness.
However, blk_mq_tag_busy() is just one shot thing, and very short time
of unfairness shouldn't be a big deal.
Looks you guys care this change, I will avoid this kind of change in V2.
Thanks,
Ming
