blk-mq: allow changing of queue depth through sysfs

For request_fn based devices, the block layer exports a 'nr_requests'
file through sysfs to allow adjusting of queue depth on the fly.
Currently this returns -EINVAL for blk-mq, since it's not wired up.
Wire this up for blk-mq, so that it now also always dynamic
adjustments of the allowed queue depth for any given block device
managed by blk-mq.

Signed-off-by: Jens Axboe <axboe@fb.com>

7 files changed, 133 insertions, 59 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index a6bd3e702201..fe81e19099a1 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -848,6 +848,47 @@ static void freed_request(struct request_list *rl, unsigned int flags)
                 __freed_request(rl, sync ^ 1);
 }
 
+int blk_update_nr_requests(struct request_queue *q, unsigned int nr)
+{
+        struct request_list *rl;
+
+        spin_lock_irq(q->queue_lock);
+        q->nr_requests = nr;
+        blk_queue_congestion_threshold(q);
+
+        /* congestion isn't cgroup aware and follows root blkcg for now */
+        rl = &q->root_rl;
+
+        if (rl->count[BLK_RW_SYNC] >= queue_congestion_on_threshold(q))
+                blk_set_queue_congested(q, BLK_RW_SYNC);
+        else if (rl->count[BLK_RW_SYNC] < queue_congestion_off_threshold(q))
+                blk_clear_queue_congested(q, BLK_RW_SYNC);
+
+        if (rl->count[BLK_RW_ASYNC] >= queue_congestion_on_threshold(q))
+                blk_set_queue_congested(q, BLK_RW_ASYNC);
+        else if (rl->count[BLK_RW_ASYNC] < queue_congestion_off_threshold(q))
+                blk_clear_queue_congested(q, BLK_RW_ASYNC);
+
+        blk_queue_for_each_rl(rl, q) {
+                if (rl->count[BLK_RW_SYNC] >= q->nr_requests) {
+                        blk_set_rl_full(rl, BLK_RW_SYNC);
+                } else {
+                        blk_clear_rl_full(rl, BLK_RW_SYNC);
+                        wake_up(&rl->wait[BLK_RW_SYNC]);
+                }
+
+                if (rl->count[BLK_RW_ASYNC] >= q->nr_requests) {
+                        blk_set_rl_full(rl, BLK_RW_ASYNC);
+                } else {
+                        blk_clear_rl_full(rl, BLK_RW_ASYNC);
+                        wake_up(&rl->wait[BLK_RW_ASYNC]);
+                }
+        }
+
+        spin_unlock_irq(q->queue_lock);
+        return 0;
+}
+
 /*
  * Determine if elevator data should be initialized when allocating the
  * request associated with @bio.
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index e6b3fbae9862..f6dea968b710 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -57,23 +57,13 @@ bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 }
 
 /*
- * If a previously busy queue goes inactive, potential waiters could now
- * be allowed to queue. Wake them up and check.
+ * Wakeup all potentially sleeping on normal (non-reserved) tags
  */
-void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
+static void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags)
 {
-        struct blk_mq_tags *tags = hctx->tags;
         struct blk_mq_bitmap_tags *bt;
         int i, wake_index;
 
-        if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
-                return;
-
-        atomic_dec(&tags->active_queues);
-
-        /*
-         * Will only throttle depth on non-reserved tags
-         */
         bt = &tags->bitmap_tags;
         wake_index = bt->wake_index;
         for (i = 0; i < BT_WAIT_QUEUES; i++) {
@@ -87,6 +77,22 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 }
 
 /*
+ * If a previously busy queue goes inactive, potential waiters could now
+ * be allowed to queue. Wake them up and check.
+ */
+void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
+{
+        struct blk_mq_tags *tags = hctx->tags;
+
+        if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+                return;
+
+        atomic_dec(&tags->active_queues);
+
+        blk_mq_tag_wakeup_all(tags);
+}
+
+/*
  * For shared tag users, we track the number of currently active users
  * and attempt to provide a fair share of the tag depth for each of them.
  */
@@ -408,6 +414,28 @@ static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt)
         return bt->depth - used;
 }
 
+static void bt_update_count(struct blk_mq_bitmap_tags *bt,
+                            unsigned int depth)
+{
+        unsigned int tags_per_word = 1U << bt->bits_per_word;
+        unsigned int map_depth = depth;
+
+        if (depth) {
+                int i;
+
+                for (i = 0; i < bt->map_nr; i++) {
+                        bt->map[i].depth = min(map_depth, tags_per_word);
+                        map_depth -= bt->map[i].depth;
+                }
+        }
+
+        bt->wake_cnt = BT_WAIT_BATCH;
+        if (bt->wake_cnt > depth / 4)
+                bt->wake_cnt = max(1U, depth / 4);
+
+        bt->depth = depth;
+}
+
 static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
                         int node, bool reserved)
 {
@@ -420,7 +448,7 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
          * condition.
          */
         if (depth) {
-                unsigned int nr, i, map_depth, tags_per_word;
+                unsigned int nr, tags_per_word;
 
                 tags_per_word = (1 << bt->bits_per_word);
 
@@ -444,11 +472,6 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
                         return -ENOMEM;
 
                 bt->map_nr = nr;
-                map_depth = depth;
-                for (i = 0; i < nr; i++) {
-                        bt->map[i].depth = min(map_depth, tags_per_word);
-                        map_depth -= tags_per_word;
-                }
         }
 
         bt->bs = kzalloc(BT_WAIT_QUEUES * sizeof(*bt->bs), GFP_KERNEL);
@@ -460,11 +483,7 @@ static int bt_alloc(struct blk_mq_bitmap_tags *bt, unsigned int depth,
         for (i = 0; i < BT_WAIT_QUEUES; i++)
                 init_waitqueue_head(&bt->bs[i].wait);
 
-        bt->wake_cnt = BT_WAIT_BATCH;
-        if (bt->wake_cnt > depth / 4)
-                bt->wake_cnt = max(1U, depth / 4);
-
-        bt->depth = depth;
+        bt_update_count(bt, depth);
         return 0;
 }
 
@@ -525,6 +544,21 @@ void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *tag)
         *tag = prandom_u32() % depth;
 }
 
+int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int tdepth)
+{
+        tdepth -= tags->nr_reserved_tags;
+        if (tdepth > tags->nr_tags)
+                return -EINVAL;
+
+        /*
+         * Don't need (or can't) update reserved tags here, they remain
+         * static and should never need resizing.
+         */
+        bt_update_count(&tags->bitmap_tags, tdepth);
+        blk_mq_tag_wakeup_all(tags);
+        return 0;
+}
+
 ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
 {
         char *orig_page = page;
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index e144f68ec45f..e7ff5ceeeb97 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -55,6 +55,7 @@ extern void blk_mq_tag_busy_iter(struct blk_mq_tags *tags, void (*fn)(void *data
 extern bool blk_mq_has_free_tags(struct blk_mq_tags *tags);
 extern ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page);
 extern void blk_mq_tag_init_last_tag(struct blk_mq_tags *tags, unsigned int *last_tag);
+extern int blk_mq_tag_update_depth(struct blk_mq_tags *tags, unsigned int depth);
 
 enum {
         BLK_MQ_TAG_CACHE_MIN    = 1,
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 0fbef7e9bef1..7b71ab1b1536 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1789,6 +1789,28 @@ 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)
+{
+        struct blk_mq_tag_set *set = q->tag_set;
+        struct blk_mq_hw_ctx *hctx;
+        int i, ret;
+
+        if (!set || nr > set->queue_depth)
+                return -EINVAL;
+
+        ret = 0;
+        queue_for_each_hw_ctx(q, hctx, i) {
+                ret = blk_mq_tag_update_depth(hctx->tags, nr);
+                if (ret)
+                        break;
+        }
+
+        if (!ret)
+                q->nr_requests = nr;
+
+        return ret;
+}
+
 void blk_mq_disable_hotplug(void)
 {
         mutex_lock(&all_q_mutex);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 5e5a378962b7..7db4fe4bd002 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -32,6 +32,7 @@ void blk_mq_drain_queue(struct request_queue *q);
 void blk_mq_free_queue(struct request_queue *q);
 void blk_mq_clone_flush_request(struct request *flush_rq,
                 struct request *orig_rq);
+int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr);
 
 /*
  * CPU hotplug helpers
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 7500f876dae4..4d6811ac13fd 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -48,11 +48,10 @@ static ssize_t queue_requests_show(struct request_queue *q, char *page)
 static ssize_t
 queue_requests_store(struct request_queue *q, const char *page, size_t count)
 {
-        struct request_list *rl;
         unsigned long nr;
-        int ret;
+        int ret, err;
 
-        if (!q->request_fn)
+        if (!q->request_fn && !q->mq_ops)
                 return -EINVAL;
 
         ret = queue_var_store(&nr, page, count);
@@ -62,40 +61,14 @@ queue_requests_store(struct request_queue *q, const char *page, size_t count)
         if (nr < BLKDEV_MIN_RQ)
                 nr = BLKDEV_MIN_RQ;
 
-        spin_lock_irq(q->queue_lock);
-        q->nr_requests = nr;
-        blk_queue_congestion_threshold(q);
-
-        /* congestion isn't cgroup aware and follows root blkcg for now */
-        rl = &q->root_rl;
-
-        if (rl->count[BLK_RW_SYNC] >= queue_congestion_on_threshold(q))
-                blk_set_queue_congested(q, BLK_RW_SYNC);
-        else if (rl->count[BLK_RW_SYNC] < queue_congestion_off_threshold(q))
-                blk_clear_queue_congested(q, BLK_RW_SYNC);
-
-        if (rl->count[BLK_RW_ASYNC] >= queue_congestion_on_threshold(q))
-                blk_set_queue_congested(q, BLK_RW_ASYNC);
-        else if (rl->count[BLK_RW_ASYNC] < queue_congestion_off_threshold(q))
-                blk_clear_queue_congested(q, BLK_RW_ASYNC);
-
-        blk_queue_for_each_rl(rl, q) {
-                if (rl->count[BLK_RW_SYNC] >= q->nr_requests) {
-                        blk_set_rl_full(rl, BLK_RW_SYNC);
-                } else {
-                        blk_clear_rl_full(rl, BLK_RW_SYNC);
-                        wake_up(&rl->wait[BLK_RW_SYNC]);
-                }
-
-                if (rl->count[BLK_RW_ASYNC] >= q->nr_requests) {
-                        blk_set_rl_full(rl, BLK_RW_ASYNC);
-                } else {
-                        blk_clear_rl_full(rl, BLK_RW_ASYNC);
-                        wake_up(&rl->wait[BLK_RW_ASYNC]);
-                }
-        }
+        if (q->request_fn)
+                err = blk_update_nr_requests(q, nr);
+        else
+                err = blk_mq_update_nr_requests(q, nr);
+
+        if (err)
+                return err;
 
-        spin_unlock_irq(q->queue_lock);
         return ret;
 }
 
diff --git a/block/blk.h b/block/blk.h
index 95cab70000e3..45385e9abf6f 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -188,6 +188,8 @@ static inline int queue_congestion_off_threshold(struct request_queue *q)
         return q->nr_congestion_off;
 }
 
+extern int blk_update_nr_requests(struct request_queue *, unsigned int);
+
 /*
  * Contribute to IO statistics IFF:
  *