On Sat, Dec 3, 2016 at 11:15 AM, Jens Axboe <axboe@xxxxxx> wrote:
> No functional changes with this patch, it's just in preparation for
> supporting legacy schedulers on blk-mq.
>
> Signed-off-by: Jens Axboe <axboe@xxxxxx>
> ---
> block/blk-core.c | 2 +-
> block/blk-exec.c | 2 +-
> block/blk-flush.c | 26 ++++++++++++++------------
> block/blk.h | 12 +++++++++++-
> 4 files changed, 27 insertions(+), 15 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 3f2eb8d80189..0e23589ab3bf 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1310,7 +1310,7 @@ static struct request *blk_old_get_request(struct request_queue *q, int rw,
>
> struct request *blk_get_request(struct request_queue *q, int rw, gfp_t gfp_mask)
> {
> - if (q->mq_ops)
> + if (blk_use_mq_path(q))
> return blk_mq_alloc_request(q, rw,
> (gfp_mask & __GFP_DIRECT_RECLAIM) ?
> 0 : BLK_MQ_REQ_NOWAIT);
Another way might be to use mq allocator to allocate rq in case of mq_sched,
such as: just replace mempool_alloc in __get_request() with
blk_mq_alloc_request(), in this way, it should be possible to
avoid one extra rq allocation in blk_mq_sched_dispatch(), and keep mq's benefit
of rq preallocation, which can avoid to hold queue_lock during the
allocation too.
> diff --git a/block/blk-exec.c b/block/blk-exec.c
> index 3ecb00a6cf45..73b8a701ae6d 100644
> --- a/block/blk-exec.c
> +++ b/block/blk-exec.c
> @@ -64,7 +64,7 @@ void blk_execute_rq_nowait(struct request_queue *q, struct gendisk *bd_disk,
> * don't check dying flag for MQ because the request won't
> * be reused after dying flag is set
> */
> - if (q->mq_ops) {
> + if (blk_use_mq_path(q)) {
> blk_mq_insert_request(rq, at_head, true, false);
> return;
> }
> diff --git a/block/blk-flush.c b/block/blk-flush.c
> index 1bdbb3d3e5f5..0b68a1258bdd 100644
> --- a/block/blk-flush.c
> +++ b/block/blk-flush.c
> @@ -133,14 +133,16 @@ static void blk_flush_restore_request(struct request *rq)
>
> static bool blk_flush_queue_rq(struct request *rq, bool add_front)
> {
> - if (rq->q->mq_ops) {
> + struct request_queue *q = rq->q;
> +
> + if (blk_use_mq_path(q)) {
> blk_mq_add_to_requeue_list(rq, add_front, true);
> return false;
> } else {
> if (add_front)
> - list_add(&rq->queuelist, &rq->q->queue_head);
> + list_add(&rq->queuelist, &q->queue_head);
> else
> - list_add_tail(&rq->queuelist, &rq->q->queue_head);
> + list_add_tail(&rq->queuelist, &q->queue_head);
> return true;
> }
> }
> @@ -201,7 +203,7 @@ static bool blk_flush_complete_seq(struct request *rq,
> BUG_ON(!list_empty(&rq->queuelist));
> list_del_init(&rq->flush.list);
> blk_flush_restore_request(rq);
> - if (q->mq_ops)
> + if (blk_use_mq_path(q))
> blk_mq_end_request(rq, error);
> else
> __blk_end_request_all(rq, error);
> @@ -224,7 +226,7 @@ static void flush_end_io(struct request *flush_rq, int error)
> unsigned long flags = 0;
> struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
>
> - if (q->mq_ops) {
> + if (blk_use_mq_path(q)) {
> struct blk_mq_hw_ctx *hctx;
>
> /* release the tag's ownership to the req cloned from */
> @@ -240,7 +242,7 @@ static void flush_end_io(struct request *flush_rq, int error)
> /* account completion of the flush request */
> fq->flush_running_idx ^= 1;
>
> - if (!q->mq_ops)
> + if (!blk_use_mq_path(q))
> elv_completed_request(q, flush_rq);
>
> /* and push the waiting requests to the next stage */
> @@ -267,7 +269,7 @@ static void flush_end_io(struct request *flush_rq, int error)
> blk_run_queue_async(q);
> }
> fq->flush_queue_delayed = 0;
> - if (q->mq_ops)
> + if (blk_use_mq_path(q))
> spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
> }
>
> @@ -315,7 +317,7 @@ static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
> * be in flight at the same time. And acquire the tag's
> * ownership for flush req.
> */
> - if (q->mq_ops) {
> + if (blk_use_mq_path(q)) {
> struct blk_mq_hw_ctx *hctx;
>
> flush_rq->mq_ctx = first_rq->mq_ctx;
> @@ -409,7 +411,7 @@ void blk_insert_flush(struct request *rq)
> * complete the request.
> */
> if (!policy) {
> - if (q->mq_ops)
> + if (blk_use_mq_path(q))
> blk_mq_end_request(rq, 0);
> else
> __blk_end_bidi_request(rq, 0, 0, 0);
> @@ -425,9 +427,9 @@ void blk_insert_flush(struct request *rq)
> */
> if ((policy & REQ_FSEQ_DATA) &&
> !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
> - if (q->mq_ops) {
> + if (blk_use_mq_path(q))
> blk_mq_insert_request(rq, false, false, true);
> - } else
> + else
> list_add_tail(&rq->queuelist, &q->queue_head);
> return;
> }
> @@ -440,7 +442,7 @@ void blk_insert_flush(struct request *rq)
> INIT_LIST_HEAD(&rq->flush.list);
> rq->rq_flags |= RQF_FLUSH_SEQ;
> rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
> - if (q->mq_ops) {
> + if (blk_use_mq_path(q)) {
> rq->end_io = mq_flush_data_end_io;
>
> spin_lock_irq(&fq->mq_flush_lock);
> diff --git a/block/blk.h b/block/blk.h
> index 041185e5f129..094fc10429c3 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -36,10 +36,20 @@ extern struct kmem_cache *request_cachep;
> extern struct kobj_type blk_queue_ktype;
> extern struct ida blk_queue_ida;
>
> +/*
> + * Use the MQ path if we have mq_ops, but not if we are using an IO
> + * scheduler. For the scheduler, we should use the legacy path. Only
> + * for internal use in the block layer.
> + */
> +static inline bool blk_use_mq_path(struct request_queue *q)
> +{
> + return q->mq_ops && !q->elevator;
> +}
> +
> static inline struct blk_flush_queue *blk_get_flush_queue(
> struct request_queue *q, struct blk_mq_ctx *ctx)
> {
> - if (q->mq_ops)
> + if (blk_use_mq_path(q))
> return blk_mq_map_queue(q, ctx->cpu)->fq;
> return q->fq;
> }
> --
> 2.7.4
>
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