blk-mq: save queue mapping result into ctx directly

Currently, the queue mapping result is saved in a two-dimensional
array. In the hot path, to get a hctx, we need do following:

  q->queue_hw_ctx[q->tag_set->map[type].mq_map[cpu]]

This isn't very efficient. We could save the queue mapping result into
ctx directly with different hctx type, like,

  ctx->hctxs[type]

Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

5 files changed, 9 insertions, 8 deletions

diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 140933e4a7d1..40905539afed 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -321,7 +321,7 @@ bool __blk_mq_sched_bio_merge(struct request_queue *q, struct bio *bio)
 {
         struct elevator_queue *e = q->elevator;
         struct blk_mq_ctx *ctx = blk_mq_get_ctx(q);
-        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx->cpu);
+        struct blk_mq_hw_ctx *hctx = blk_mq_map_queue(q, bio->bi_opf, ctx);
         bool ret = false;
         enum hctx_type type;
 
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 2089c6c62f44..a4931fc7be8a 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -170,7 +170,7 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 
                 data->ctx = blk_mq_get_ctx(data->q);
                 data->hctx = blk_mq_map_queue(data->q, data->cmd_flags,
-                                                data->ctx->cpu);
+                                                data->ctx);
                 tags = blk_mq_tags_from_data(data);
                 if (data->flags & BLK_MQ_REQ_RESERVED)
                         bt = &tags->breserved_tags;
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8f5b533764ca..445d0a2642ae 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -364,7 +364,7 @@ static struct request *blk_mq_get_request(struct request_queue *q,
         }
         if (likely(!data->hctx))
                 data->hctx = blk_mq_map_queue(q, data->cmd_flags,
-                                                data->ctx->cpu);
+                                                data->ctx);
         if (data->cmd_flags & REQ_NOWAIT)
                 data->flags |= BLK_MQ_REQ_NOWAIT;
 
@@ -2435,7 +2435,7 @@ static void blk_mq_map_swqueue(struct request_queue *q)
                                 continue;
 
                         hctx = blk_mq_map_queue_type(q, j, i);
-
+                        ctx->hctxs[j] = hctx;
                         /*
                          * If the CPU is already set in the mask, then we've
                          * mapped this one already. This can happen if
diff --git a/block/blk-mq.h b/block/blk-mq.h
index d943d46b0785..9fb06261518e 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -23,6 +23,7 @@ struct blk_mq_ctx {
 
         unsigned int            cpu;
         unsigned short          index_hw[HCTX_MAX_TYPES];
+        struct blk_mq_hw_ctx    *hctxs[HCTX_MAX_TYPES];
 
         /* incremented at dispatch time */
         unsigned long           rq_dispatched[2];
@@ -97,11 +98,11 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue_type(struct request_queue *
  * blk_mq_map_queue() - map (cmd_flags,type) to hardware queue
  * @q: request queue
  * @flags: request command flags
- * @cpu: CPU
+ * @cpu: cpu ctx
  */
 static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
                                                      unsigned int flags,
-                                                     unsigned int cpu)
+                                                     struct blk_mq_ctx *ctx)
 {
         enum hctx_type type = HCTX_TYPE_DEFAULT;
 
@@ -116,7 +117,7 @@ static inline struct blk_mq_hw_ctx *blk_mq_map_queue(struct request_queue *q,
                  q->tag_set->map[HCTX_TYPE_READ].nr_queues)
                 type = HCTX_TYPE_READ;
         
-        return blk_mq_map_queue_type(q, type, cpu);
+        return ctx->hctxs[type];
 }
 
 /*
diff --git a/block/blk.h b/block/blk.h
index 848278c52030..5d636ee41663 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -38,7 +38,7 @@ extern struct ida blk_queue_ida;
 static inline struct blk_flush_queue *
 blk_get_flush_queue(struct request_queue *q, struct blk_mq_ctx *ctx)
 {
-        return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx->cpu)->fq;
+        return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx)->fq;
 }
 
 static inline void __blk_get_queue(struct request_queue *q)