blk-mq: add tag allocation policy

This is the blk-mq part to support tag allocation policy. The default
allocation policy isn't changed (though it's not a strict FIFO). The new
policy is round-robin for libata. But it's a try-best implementation. If
multiple tasks are competing, the tags returned will be mixed (which is
unavoidable even with !mq, as requests from different tasks can be
mixed in queue)

Cc: Jens Axboe <axboe@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Shaohua Li <shli@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

5 files changed, 39 insertions, 17 deletions

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index d4daee385a23..e3387a74a9a2 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -140,7 +140,8 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
         return atomic_read(&hctx->nr_active) < depth;
 }
 
-static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
+static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag,
+                         bool nowrap)
 {
         int tag, org_last_tag = last_tag;
 
@@ -152,7 +153,7 @@ static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
                          * offset to 0 in a failure case, so start from 0 to
                          * exhaust the map.
                          */
-                        if (org_last_tag && last_tag) {
+                        if (org_last_tag && last_tag && !nowrap) {
                                 last_tag = org_last_tag = 0;
                                 continue;
                         }
@@ -170,6 +171,8 @@ static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
         return tag;
 }
 
+#define BT_ALLOC_RR(tags) (tags->alloc_policy == BLK_TAG_ALLOC_RR)
+
 /*
  * Straight forward bitmap tag implementation, where each bit is a tag
  * (cleared == free, and set == busy). The small twist is using per-cpu
@@ -182,7 +185,7 @@ static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
  * until the map is exhausted.
  */
 static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
-                    unsigned int *tag_cache)
+                    unsigned int *tag_cache, struct blk_mq_tags *tags)
 {
         unsigned int last_tag, org_last_tag;
         int index, i, tag;
@@ -194,7 +197,8 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
         index = TAG_TO_INDEX(bt, last_tag);
 
         for (i = 0; i < bt->map_nr; i++) {
-                tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag));
+                tag = __bt_get_word(&bt->map[index], TAG_TO_BIT(bt, last_tag),
+                                    BT_ALLOC_RR(tags));
                 if (tag != -1) {
                         tag += (index << bt->bits_per_word);
                         goto done;
@@ -221,7 +225,7 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
          * up using the specific cached tag.
          */
 done:
-        if (tag == org_last_tag) {
+        if (tag == org_last_tag || unlikely(BT_ALLOC_RR(tags))) {
                 last_tag = tag + 1;
                 if (last_tag >= bt->depth - 1)
                         last_tag = 0;
@@ -250,13 +254,13 @@ static struct bt_wait_state *bt_wait_ptr(struct blk_mq_bitmap_tags *bt,
 static int bt_get(struct blk_mq_alloc_data *data,
                 struct blk_mq_bitmap_tags *bt,
                 struct blk_mq_hw_ctx *hctx,
-                unsigned int *last_tag)
+                unsigned int *last_tag, struct blk_mq_tags *tags)
 {
         struct bt_wait_state *bs;
         DEFINE_WAIT(wait);
         int tag;
 
-        tag = __bt_get(hctx, bt, last_tag);
+        tag = __bt_get(hctx, bt, last_tag, tags);
         if (tag != -1)
                 return tag;
 
@@ -267,7 +271,7 @@ static int bt_get(struct blk_mq_alloc_data *data,
         do {
                 prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
 
-                tag = __bt_get(hctx, bt, last_tag);
+                tag = __bt_get(hctx, bt, last_tag, tags);
                 if (tag != -1)
                         break;
 
@@ -282,7 +286,7 @@ static int bt_get(struct blk_mq_alloc_data *data,
                  * Retry tag allocation after running the hardware queue,
                  * as running the queue may also have found completions.
                  */
-                tag = __bt_get(hctx, bt, last_tag);
+                tag = __bt_get(hctx, bt, last_tag, tags);
                 if (tag != -1)
                         break;
 
@@ -313,7 +317,7 @@ static unsigned int __blk_mq_get_tag(struct blk_mq_alloc_data *data)
         int tag;
 
         tag = bt_get(data, &data->hctx->tags->bitmap_tags, data->hctx,
-                        &data->ctx->last_tag);
+                        &data->ctx->last_tag, data->hctx->tags);
         if (tag >= 0)
                 return tag + data->hctx->tags->nr_reserved_tags;
 
@@ -329,7 +333,8 @@ static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_alloc_data *data)
                 return BLK_MQ_TAG_FAIL;
         }
 
-        tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero);
+        tag = bt_get(data, &data->hctx->tags->breserved_tags, NULL, &zero,
+                data->hctx->tags);
         if (tag < 0)
                 return BLK_MQ_TAG_FAIL;
 
@@ -401,7 +406,8 @@ void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
 
                 BUG_ON(real_tag >= tags->nr_tags);
                 bt_clear_tag(&tags->bitmap_tags, real_tag);
-                *last_tag = real_tag;
+                if (likely(tags->alloc_policy == BLK_TAG_ALLOC_FIFO))
+                        *last_tag = real_tag;
         } else {
                 BUG_ON(tag >= tags->nr_reserved_tags);
                 bt_clear_tag(&tags->breserved_tags, tag);
@@ -538,10 +544,12 @@ static void bt_free(struct blk_mq_bitmap_tags *bt)
 }
 
 static struct blk_mq_tags *blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
-                                                   int node)
+                                                   int node, int alloc_policy)
 {
         unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 
+        tags->alloc_policy = alloc_policy;
+
         if (bt_alloc(&tags->bitmap_tags, depth, node, false))
                 goto enomem;
         if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, node, true))
@@ -555,7 +563,8 @@ enomem:
 }
 
 struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
-                                     unsigned int reserved_tags, int node)
+                                     unsigned int reserved_tags,
+                                     int node, int alloc_policy)
 {
         struct blk_mq_tags *tags;
 
@@ -571,7 +580,7 @@ struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
         tags->nr_tags = total_tags;
         tags->nr_reserved_tags = reserved_tags;
 
-        return blk_mq_init_bitmap_tags(tags, node);
+        return blk_mq_init_bitmap_tags(tags, node, alloc_policy);
 }
 
 void blk_mq_free_tags(struct blk_mq_tags *tags)
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index a6fa0fc9d41a..90767b370308 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -42,10 +42,12 @@ struct blk_mq_tags {
 
         struct request **rqs;
         struct list_head page_list;
+
+        int alloc_policy;
 };
 
 
-extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node);
+extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node, int alloc_policy);
 extern void blk_mq_free_tags(struct blk_mq_tags *tags);
 
 extern unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index a7d4a988516f..eb8e694fda06 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1374,7 +1374,8 @@ static struct blk_mq_tags *blk_mq_init_rq_map(struct blk_mq_tag_set *set,
         size_t rq_size, left;
 
         tags = blk_mq_init_tags(set->queue_depth, set->reserved_tags,
-                                set->numa_node);
+                                set->numa_node,
+                                BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
         if (!tags)
                 return NULL;
 
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 9ea95dd3e260..49ab11508286 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -2188,6 +2188,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
         shost->tag_set.cmd_size = cmd_size;
         shost->tag_set.numa_node = NUMA_NO_NODE;
         shost->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
+        shost->tag_set.flags |=
+                BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
         shost->tag_set.driver_data = shost;
 
         return blk_mq_alloc_tag_set(&shost->tag_set);
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 5b6500c77ed2..86b08b1a5eba 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -147,6 +147,8 @@ enum {
         BLK_MQ_F_SG_MERGE       = 1 << 2,
         BLK_MQ_F_SYSFS_UP       = 1 << 3,
         BLK_MQ_F_DEFER_ISSUE    = 1 << 4,
+        BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,
+        BLK_MQ_F_ALLOC_POLICY_BITS = 1,
 
         BLK_MQ_S_STOPPED        = 0,
         BLK_MQ_S_TAG_ACTIVE     = 1,
@@ -155,6 +157,12 @@ enum {
 
         BLK_MQ_CPU_WORK_BATCH   = 8,
 };
+#define BLK_MQ_FLAG_TO_ALLOC_POLICY(flags) \
+        ((flags >> BLK_MQ_F_ALLOC_POLICY_START_BIT) & \
+                ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1))
+#define BLK_ALLOC_POLICY_TO_MQ_FLAG(policy) \
+        ((policy & ((1 << BLK_MQ_F_ALLOC_POLICY_BITS) - 1)) \
+                << BLK_MQ_F_ALLOC_POLICY_START_BIT)
 
 struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *);
 void blk_mq_finish_init(struct request_queue *q);