SCSI sets q->queue_depth from shost->cmd_per_lun, and
q->queue_depth is per request_queue and more related to
scheduler queue compared with hw queue depth, which can be
shared by queues, such as TAG_SHARED.

This patch trys to use q->queue_depth as hint for computing
q->nr_requests, which should be more effective than
current way.

Signed-off-by: Ming Lei <ming....@redhat.com>
---
 block/blk-mq-sched.h | 18 +++++++++++++++---
 block/blk-mq.c       | 27 +++++++++++++++++++++++++--
 block/blk-mq.h       |  1 +
 block/blk-settings.c |  2 ++
 4 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/block/blk-mq-sched.h b/block/blk-mq-sched.h
index 1d47f3fda1d0..bb772e680e01 100644
--- a/block/blk-mq-sched.h
+++ b/block/blk-mq-sched.h
@@ -99,12 +99,24 @@ static inline bool blk_mq_sched_needs_restart(struct 
blk_mq_hw_ctx *hctx)
 static inline unsigned blk_mq_sched_queue_depth(struct request_queue *q)
 {
        /*
-        * Default to double of smaller one between hw queue_depth and 128,
+        * q->queue_depth is more close to scheduler queue, so use it
+        * as hint for computing scheduler queue depth if it is valid
+        */
+       unsigned q_depth = q->queue_depth ?: q->tag_set->queue_depth;
+
+       /*
+        * Default to double of smaller one between queue depth and 128,
         * since we don't split into sync/async like the old code did.
         * Additionally, this is a per-hw queue depth.
         */
-       return 2 * min_t(unsigned int, q->tag_set->queue_depth,
-                                  BLKDEV_MAX_RQ);
+       q_depth = 2 * min_t(unsigned int, q_depth, BLKDEV_MAX_RQ);
+
+       /*
+        * when queue depth of driver is too small, we set queue depth
+        * of scheduler queue as 32 so that small queue device still
+        * can benefit from IO merging.
+        */
+       return max_t(unsigned, q_depth, 32);
 }
 
 #endif
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 041f7b7fa0d6..cbb005834a94 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2558,7 +2558,9 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 }
 EXPORT_SYMBOL(blk_mq_free_tag_set);
 
-int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
+static int __blk_mq_update_nr_requests(struct request_queue *q,
+                                      bool sched_only,
+                                      unsigned int nr)
 {
        struct blk_mq_tag_set *set = q->tag_set;
        struct blk_mq_hw_ctx *hctx;
@@ -2577,7 +2579,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, 
unsigned int nr)
                 * If we're using an MQ scheduler, just update the scheduler
                 * queue depth. This is similar to what the old code would do.
                 */
-               if (!hctx->sched_tags) {
+               if (!sched_only && !hctx->sched_tags) {
                        ret = blk_mq_tag_update_depth(hctx, &hctx->tags,
                                                        min(nr, 
set->queue_depth),
                                                        false);
@@ -2597,6 +2599,27 @@ int blk_mq_update_nr_requests(struct request_queue *q, 
unsigned int nr)
        return ret;
 }
 
+int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
+{
+       return __blk_mq_update_nr_requests(q, false, nr);
+}
+
+/*
+ * When drivers update q->queue_depth, this API is called so that
+ * we can use this queue depth as hint for adjusting scheduler
+ * queue depth.
+ */
+int blk_mq_update_sched_queue_depth(struct request_queue *q)
+{
+       unsigned nr;
+
+       if (!q->mq_ops || !q->elevator)
+               return 0;
+
+       nr = blk_mq_sched_queue_depth(q);
+       return __blk_mq_update_nr_requests(q, true, nr);
+}
+
 static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set,
                                                        int nr_hw_queues)
 {
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 60b01c0309bc..c2c1a2a82999 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -35,6 +35,7 @@ void blk_mq_flush_busy_ctxs(struct blk_mq_hw_ctx *hctx, 
struct list_head *list);
 bool blk_mq_hctx_has_pending(struct blk_mq_hw_ctx *hctx);
 bool blk_mq_get_driver_tag(struct request *rq, struct blk_mq_hw_ctx **hctx,
                                bool wait);
+int blk_mq_update_sched_queue_depth(struct request_queue *q);
 
 /*
  * Internal helpers for allocating/freeing the request map
diff --git a/block/blk-settings.c b/block/blk-settings.c
index be1f115b538b..94a349601545 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -877,6 +877,8 @@ void blk_set_queue_depth(struct request_queue *q, unsigned 
int depth)
 {
        q->queue_depth = depth;
        wbt_set_queue_depth(q->rq_wb, depth);
+
+       WARN_ON(blk_mq_update_sched_queue_depth(q));
 }
 EXPORT_SYMBOL(blk_set_queue_depth);
 
-- 
2.9.4

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