blk-mq: don't allocate driver tag upfront for flush rq
The idea behind it is simple: 1) for none scheduler, driver tag has to be borrowed for flush rq, otherwise we may run out of tag, and that causes an IO hang. And get/put driver tag is actually noop for none, so reordering tags isn't necessary at all. 2) for a real I/O scheduler, we need not allocate a driver tag upfront for flush rq. It works just fine to follow the same approach as normal requests: allocate driver tag for each rq just before calling ->queue_rq(). One driver visible change is that the driver tag isn't shared in the flush request sequence. That won't be a problem, since we always do that in legacy path. Then flush rq need not be treated specially wrt. get/put driver tag. This cleans up the code - for instance, reorder_tags_to_front() can be removed, and we needn't worry about request ordering in dispatch list for avoiding I/O deadlock. Also we have to put the driver tag before requeueing. Signed-off-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei
Jens Axboe
Родитель
244c65a3cc
Коммит
923218f616
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@ -231,8 +231,13 @@ static void flush_end_io(struct request *flush_rq, blk_status_t error)
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/* release the tag's ownership to the req cloned from */
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spin_lock_irqsave(&fq->mq_flush_lock, flags);
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hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);
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blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
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flush_rq->tag = -1;
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if (!q->elevator) {
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blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
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flush_rq->tag = -1;
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} else {
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blk_mq_put_driver_tag_hctx(hctx, flush_rq);
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flush_rq->internal_tag = -1;
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}
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}
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running = &fq->flush_queue[fq->flush_running_idx];
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@ -318,19 +323,26 @@ static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
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blk_rq_init(q, flush_rq);
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/*
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* Borrow tag from the first request since they can't
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* be in flight at the same time. And acquire the tag's
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* ownership for flush req.
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* In case of none scheduler, borrow tag from the first request
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* since they can't be in flight at the same time. And acquire
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* the tag's ownership for flush req.
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*
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* In case of IO scheduler, flush rq need to borrow scheduler tag
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* just for cheating put/get driver tag.
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*/
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if (q->mq_ops) {
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struct blk_mq_hw_ctx *hctx;
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flush_rq->mq_ctx = first_rq->mq_ctx;
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flush_rq->tag = first_rq->tag;
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fq->orig_rq = first_rq;
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hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
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blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
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if (!q->elevator) {
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fq->orig_rq = first_rq;
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flush_rq->tag = first_rq->tag;
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hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
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blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
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} else {
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flush_rq->internal_tag = first_rq->internal_tag;
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}
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}
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flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
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@ -394,6 +406,11 @@ static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
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hctx = blk_mq_map_queue(q, ctx->cpu);
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if (q->elevator) {
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WARN_ON(rq->tag < 0);
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blk_mq_put_driver_tag_hctx(hctx, rq);
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}
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/*
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* After populating an empty queue, kick it to avoid stall. Read
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* the comment in flush_end_io().
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@ -356,29 +356,12 @@ static bool blk_mq_sched_bypass_insert(struct blk_mq_hw_ctx *hctx,
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return true;
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}
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if (has_sched) {
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if (has_sched)
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rq->rq_flags |= RQF_SORTED;
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WARN_ON(rq->tag != -1);
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}
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return false;
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}
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/*
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* Add flush/fua to the queue. If we fail getting a driver tag, then
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* punt to the requeue list. Requeue will re-invoke us from a context
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* that's safe to block from.
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*/
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static void blk_mq_sched_insert_flush(struct blk_mq_hw_ctx *hctx,
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struct request *rq, bool can_block)
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{
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if (blk_mq_get_driver_tag(rq, &hctx, can_block)) {
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blk_insert_flush(rq);
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blk_mq_run_hw_queue(hctx, true);
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} else
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blk_mq_add_to_requeue_list(rq, false, true);
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}
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void blk_mq_sched_insert_request(struct request *rq, bool at_head,
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bool run_queue, bool async, bool can_block)
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{
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@ -389,10 +372,12 @@ void blk_mq_sched_insert_request(struct request *rq, bool at_head,
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/* flush rq in flush machinery need to be dispatched directly */
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if (!(rq->rq_flags & RQF_FLUSH_SEQ) && op_is_flush(rq->cmd_flags)) {
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blk_mq_sched_insert_flush(hctx, rq, can_block);
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return;
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blk_insert_flush(rq);
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goto run;
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}
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WARN_ON(e && (rq->tag != -1));
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if (blk_mq_sched_bypass_insert(hctx, !!e, rq))
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goto run;
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@ -419,23 +404,6 @@ void blk_mq_sched_insert_requests(struct request_queue *q,
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struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, ctx->cpu);
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struct elevator_queue *e = hctx->queue->elevator;
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if (e) {
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struct request *rq, *next;
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/*
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* We bypass requests that already have a driver tag assigned,
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* which should only be flushes. Flushes are only ever inserted
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* as single requests, so we shouldn't ever hit the
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* WARN_ON_ONCE() below (but let's handle it just in case).
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*/
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list_for_each_entry_safe(rq, next, list, queuelist) {
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if (WARN_ON_ONCE(rq->tag != -1)) {
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list_del_init(&rq->queuelist);
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blk_mq_sched_bypass_insert(hctx, true, rq);
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}
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}
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}
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if (e && e->type->ops.mq.insert_requests)
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e->type->ops.mq.insert_requests(hctx, list, false);
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else
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@ -653,6 +653,8 @@ static void __blk_mq_requeue_request(struct request *rq)
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{
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struct request_queue *q = rq->q;
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blk_mq_put_driver_tag(rq);
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trace_block_rq_requeue(q, rq);
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wbt_requeue(q->rq_wb, &rq->issue_stat);
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blk_mq_sched_requeue_request(rq);
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@ -996,30 +998,6 @@ done:
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return rq->tag != -1;
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}
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/*
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* If we fail getting a driver tag because all the driver tags are already
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* assigned and on the dispatch list, BUT the first entry does not have a
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* tag, then we could deadlock. For that case, move entries with assigned
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* driver tags to the front, leaving the set of tagged requests in the
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* same order, and the untagged set in the same order.
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*/
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static bool reorder_tags_to_front(struct list_head *list)
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{
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struct request *rq, *tmp, *first = NULL;
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list_for_each_entry_safe_reverse(rq, tmp, list, queuelist) {
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if (rq == first)
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break;
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if (rq->tag != -1) {
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list_move(&rq->queuelist, list);
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if (!first)
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first = rq;
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}
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}
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return first != NULL;
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}
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static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode, int flags,
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void *key)
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{
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@ -1080,9 +1058,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
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rq = list_first_entry(list, struct request, queuelist);
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if (!blk_mq_get_driver_tag(rq, &hctx, false)) {
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if (!queued && reorder_tags_to_front(list))
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continue;
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/*
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* The initial allocation attempt failed, so we need to
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* rerun the hardware queue when a tag is freed.
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@ -1133,7 +1108,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
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nxt = list_first_entry(list, struct request, queuelist);
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blk_mq_put_driver_tag(nxt);
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}
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blk_mq_put_driver_tag_hctx(hctx, rq);
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list_add(&rq->queuelist, list);
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__blk_mq_requeue_request(rq);
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break;
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@ -1698,13 +1672,10 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
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if (unlikely(is_flush_fua)) {
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blk_mq_put_ctx(data.ctx);
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blk_mq_bio_to_request(rq, bio);
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if (q->elevator) {
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blk_mq_sched_insert_request(rq, false, true, true,
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true);
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} else {
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blk_insert_flush(rq);
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blk_mq_run_hw_queue(data.hctx, true);
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}
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/* bypass scheduler for flush rq */
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blk_insert_flush(rq);
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blk_mq_run_hw_queue(data.hctx, true);
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} else if (plug && q->nr_hw_queues == 1) {
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struct request *last = NULL;
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