When blk-mq I/O scheduler is used, we need two tags for submitting one request. One is called scheduler tag for allocating request and scheduling I/O, another one is called driver tag, which is used for dispatching IO to hardware/driver. This way introduces one extra per-queue allocation for both tags and request pool, and may not be as efficient as case of none scheduler.
Also currently we put a default per-hctx limit on schedulable requests, and this limit may be a bottleneck for some devices, especialy when these devices have a quite big tag space. This patch introduces BLK_MQ_F_SCHED_USE_HW_TAG so that we can allow to use hardware/driver tags directly for IO scheduling if devices's hardware tag space is big enough. Then we can avoid the extra resource allocation and make IO submission more efficient. Signed-off-by: Ming Lei <ming....@redhat.com> --- block/blk-mq-sched.c | 10 +++++++++- block/blk-mq.c | 35 +++++++++++++++++++++++++++++------ include/linux/blk-mq.h | 1 + 3 files changed, 39 insertions(+), 7 deletions(-) diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c index 27c67465f856..45a675f07b8b 100644 --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -83,7 +83,12 @@ struct request *blk_mq_sched_get_request(struct request_queue *q, data->hctx = blk_mq_map_queue(q, data->ctx->cpu); if (e) { - data->flags |= BLK_MQ_REQ_INTERNAL; + /* + * If BLK_MQ_F_SCHED_USE_HW_TAG is set, we use hardware + * tag for IO scheduler directly. + */ + if (!(data->hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG)) + data->flags |= BLK_MQ_REQ_INTERNAL; /* * Flush requests are special and go directly to the @@ -431,6 +436,9 @@ static int blk_mq_sched_alloc_tags(struct request_queue *q, struct blk_mq_tag_set *set = q->tag_set; int ret; + if (hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG) + return 0; + hctx->sched_tags = blk_mq_alloc_rq_map(set, hctx_idx, q->nr_requests, set->reserved_tags); if (!hctx->sched_tags) diff --git a/block/blk-mq.c b/block/blk-mq.c index 0168b27469cb..e530bc54f0d9 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -263,9 +263,19 @@ struct request *__blk_mq_alloc_request(struct blk_mq_alloc_data *data, rq->rq_flags = RQF_MQ_INFLIGHT; atomic_inc(&data->hctx->nr_active); } - rq->tag = tag; - rq->internal_tag = -1; - data->hctx->tags->rqs[rq->tag] = rq; + data->hctx->tags->rqs[tag] = rq; + + /* + * If we use hw tag for scheduling, postpone setting + * rq->tag in blk_mq_get_driver_tag(). + */ + if (data->hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG) { + rq->tag = -1; + rq->internal_tag = tag; + } else { + rq->tag = tag; + rq->internal_tag = -1; + } } if (data->flags & BLK_MQ_REQ_RESERVED) @@ -368,7 +378,7 @@ void __blk_mq_finish_request(struct blk_mq_hw_ctx *hctx, struct blk_mq_ctx *ctx, clear_bit(REQ_ATOM_POLL_SLEPT, &rq->atomic_flags); if (rq->tag != -1) blk_mq_put_tag(hctx, hctx->tags, ctx, rq->tag); - if (sched_tag != -1) + if (sched_tag != -1 && !(hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG)) blk_mq_put_tag(hctx, hctx->sched_tags, ctx, sched_tag); blk_mq_sched_restart(hctx); blk_queue_exit(q); @@ -872,6 +882,12 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx, if (rq->tag != -1) goto done; + /* we buffered driver tag in rq->internal_tag */ + if (data.hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG) { + rq->tag = rq->internal_tag; + goto done; + } + if (blk_mq_tag_is_reserved(data.hctx->sched_tags, rq->internal_tag)) data.flags |= BLK_MQ_REQ_RESERVED; @@ -893,9 +909,15 @@ bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx, static void __blk_mq_put_driver_tag(struct blk_mq_hw_ctx *hctx, struct request *rq) { - blk_mq_put_tag(hctx, hctx->tags, rq->mq_ctx, rq->tag); + unsigned tag = rq->tag; + rq->tag = -1; + if (hctx->flags & BLK_MQ_F_SCHED_USE_HW_TAG) + return; + + blk_mq_put_tag(hctx, hctx->tags, rq->mq_ctx, tag); + if (rq->rq_flags & RQF_MQ_INFLIGHT) { rq->rq_flags &= ~RQF_MQ_INFLIGHT; atomic_dec(&hctx->nr_active); @@ -2865,7 +2887,8 @@ bool blk_mq_poll(struct request_queue *q, blk_qc_t cookie) blk_flush_plug_list(plug, false); hctx = q->queue_hw_ctx[blk_qc_t_to_queue_num(cookie)]; - if (!blk_qc_t_is_internal(cookie)) + if (!blk_qc_t_is_internal(cookie) || (hctx->flags & + BLK_MQ_F_SCHED_USE_HW_TAG)) rq = blk_mq_tag_to_rq(hctx->tags, blk_qc_t_to_tag(cookie)); else { rq = blk_mq_tag_to_rq(hctx->sched_tags, blk_qc_t_to_tag(cookie)); diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h index 32bd8eb5ba67..53f24df91a05 100644 --- a/include/linux/blk-mq.h +++ b/include/linux/blk-mq.h @@ -162,6 +162,7 @@ enum { BLK_MQ_F_SG_MERGE = 1 << 2, BLK_MQ_F_BLOCKING = 1 << 5, BLK_MQ_F_NO_SCHED = 1 << 6, + BLK_MQ_F_SCHED_USE_HW_TAG = 1 << 7, BLK_MQ_F_ALLOC_POLICY_START_BIT = 8, BLK_MQ_F_ALLOC_POLICY_BITS = 1, -- 2.9.3