dm: add full blk-mq support to request-based DM

Commit e5863d9ad ("dm: allocate requests in target when stacking on
blk-mq devices") served as the first step toward fully utilizing blk-mq
in request-based DM -- it enabled stacking an old-style (request_fn)
request_queue ontop of the underlying blk-mq device(s).  That first step
didn't improve performance of DM multipath ontop of fast blk-mq devices
(e.g. NVMe) because the top-level old-style request_queue was severely
limited by the queue_lock.

The second step offered here enables stacking a blk-mq request_queue
ontop of the underlying blk-mq device(s).  This unlocks significant
performance gains on fast blk-mq devices, Keith Busch tested on his NVMe
testbed and offered this really positive news:

 "Just providing a performance update. All my fio tests are getting
  roughly equal performance whether accessed through the raw block
  device or the multipath device mapper (~470k IOPS). I could only push
  ~20% of the raw iops through dm before this conversion, so this latest
  tree is looking really solid from a performance standpoint."

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Tested-by: Keith Busch <keith.busch@intel.com>

4 files changed, 261 insertions, 73 deletions

diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c
index add6391f3f8e..c8f07e5a9a17 100644
--- a/drivers/md/dm-mpath.c
+++ b/drivers/md/dm-mpath.c
@@ -1703,7 +1703,7 @@ out:
  *---------------------------------------------------------------*/
 static struct target_type multipath_target = {
         .name = "multipath",
-        .version = {1, 8, 0},
+        .version = {1, 9, 0},
         .module = THIS_MODULE,
         .ctr = multipath_ctr,
         .dtr = multipath_dtr,
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 057312048b68..66600cab9fa5 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -18,6 +18,7 @@
 #include <linux/mutex.h>
 #include <linux/delay.h>
 #include <linux/atomic.h>
+#include <linux/blk-mq.h>
 
 #define DM_MSG_PREFIX "table"
 
@@ -1695,9 +1696,13 @@ void dm_table_run_md_queue_async(struct dm_table *t)
         md = dm_table_get_md(t);
         queue = dm_get_md_queue(md);
         if (queue) {
-                spin_lock_irqsave(queue->queue_lock, flags);
-                blk_run_queue_async(queue);
-                spin_unlock_irqrestore(queue->queue_lock, flags);
+                if (queue->mq_ops)
+                        blk_mq_run_hw_queues(queue, true);
+                else {
+                        spin_lock_irqsave(queue->queue_lock, flags);
+                        blk_run_queue_async(queue);
+                        spin_unlock_irqrestore(queue->queue_lock, flags);
+                }
         }
 }
 EXPORT_SYMBOL(dm_table_run_md_queue_async);
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 5294e016e92b..3a66baac76ed 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -23,6 +23,7 @@
 #include <linux/kthread.h>
 #include <linux/ktime.h>
 #include <linux/elevator.h> /* for rq_end_sector() */
+#include <linux/blk-mq.h>
 
 #include <trace/events/block.h>
 
@@ -224,6 +225,9 @@ struct mapped_device {
         int last_rq_rw;
         sector_t last_rq_pos;
         ktime_t last_rq_start_time;
+
+        /* for blk-mq request-based DM support */
+        struct blk_mq_tag_set tag_set;
 };
 
 /*
@@ -1025,6 +1029,11 @@ static void end_clone_bio(struct bio *clone, int error)
         blk_update_request(tio->orig, 0, nr_bytes);
 }
 
+static struct dm_rq_target_io *tio_from_request(struct request *rq)
+{
+        return (rq->q->mq_ops ? blk_mq_rq_to_pdu(rq) : rq->special);
+}
+
 /*
  * Don't touch any member of the md after calling this function because
  * the md may be freed in dm_put() at the end of this function.
@@ -1048,8 +1057,10 @@ static void rq_completed(struct mapped_device *md, int rw, bool run_queue)
          * queue lock again.
          */
         if (run_queue) {
-                if (!nr_requests_pending ||
-                    (nr_requests_pending >= md->queue->nr_congestion_on))
+                if (md->queue->mq_ops)
+                        blk_mq_run_hw_queues(md->queue, true);
+                else if (!nr_requests_pending ||
+                         (nr_requests_pending >= md->queue->nr_congestion_on))
                         blk_run_queue_async(md->queue);
         }
 
@@ -1062,13 +1073,17 @@ static void rq_completed(struct mapped_device *md, int rw, bool run_queue)
 static void free_rq_clone(struct request *clone)
 {
         struct dm_rq_target_io *tio = clone->end_io_data;
+        struct mapped_device *md = tio->md;
 
         blk_rq_unprep_clone(clone);
+
         if (clone->q && clone->q->mq_ops)
                 tio->ti->type->release_clone_rq(clone);
         else
-                free_clone_request(tio->md, clone);
-        free_rq_tio(tio);
+                free_clone_request(md, clone);
+
+        if (!md->queue->mq_ops)
+                free_rq_tio(tio);
 }
 
 /*
@@ -1097,17 +1112,22 @@ static void dm_end_request(struct request *clone, int error)
         }
 
         free_rq_clone(clone);
-        blk_end_request_all(rq, error);
+        if (!rq->q->mq_ops)
+                blk_end_request_all(rq, error);
+        else
+                blk_mq_end_request(rq, error);
         rq_completed(md, rw, true);
 }
 
 static void dm_unprep_request(struct request *rq)
 {
-        struct dm_rq_target_io *tio = rq->special;
+        struct dm_rq_target_io *tio = tio_from_request(rq);
         struct request *clone = tio->clone;
 
-        rq->special = NULL;
-        rq->cmd_flags &= ~REQ_DONTPREP;
+        if (!rq->q->mq_ops) {
+                rq->special = NULL;
+                rq->cmd_flags &= ~REQ_DONTPREP;
+        }
 
         if (clone)
                 free_rq_clone(clone);
@@ -1116,18 +1136,29 @@ static void dm_unprep_request(struct request *rq)
 /*
  * Requeue the original request of a clone.
  */
-static void dm_requeue_unmapped_original_request(struct mapped_device *md,
-                                                 struct request *rq)
+static void old_requeue_request(struct request *rq)
 {
-        int rw = rq_data_dir(rq);
         struct request_queue *q = rq->q;
         unsigned long flags;
 
-        dm_unprep_request(rq);
-
         spin_lock_irqsave(q->queue_lock, flags);
         blk_requeue_request(q, rq);
         spin_unlock_irqrestore(q->queue_lock, flags);
+}
+
+static void dm_requeue_unmapped_original_request(struct mapped_device *md,
+                                                 struct request *rq)
+{
+        int rw = rq_data_dir(rq);
+
+        dm_unprep_request(rq);
+
+        if (!rq->q->mq_ops)
+                old_requeue_request(rq);
+        else {
+                blk_mq_requeue_request(rq);
+                blk_mq_kick_requeue_list(rq->q);
+        }
 
         rq_completed(md, rw, false);
 }
@@ -1139,35 +1170,44 @@ static void dm_requeue_unmapped_request(struct request *clone)
         dm_requeue_unmapped_original_request(tio->md, tio->orig);
 }
 
-static void __stop_queue(struct request_queue *q)
-{
-        blk_stop_queue(q);
-}
-
-static void stop_queue(struct request_queue *q)
+static void old_stop_queue(struct request_queue *q)
 {
         unsigned long flags;
 
+        if (blk_queue_stopped(q))
+                return;
+
         spin_lock_irqsave(q->queue_lock, flags);
-        __stop_queue(q);
+        blk_stop_queue(q);
         spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
-static void __start_queue(struct request_queue *q)
+static void stop_queue(struct request_queue *q)
 {
-        if (blk_queue_stopped(q))
-                blk_start_queue(q);
+        if (!q->mq_ops)
+                old_stop_queue(q);
+        else
+                blk_mq_stop_hw_queues(q);
 }
 
-static void start_queue(struct request_queue *q)
+static void old_start_queue(struct request_queue *q)
 {
         unsigned long flags;
 
         spin_lock_irqsave(q->queue_lock, flags);
-        __start_queue(q);
+        if (blk_queue_stopped(q))
+                blk_start_queue(q);
         spin_unlock_irqrestore(q->queue_lock, flags);
 }
 
+static void start_queue(struct request_queue *q)
+{
+        if (!q->mq_ops)
+                old_start_queue(q);
+        else
+                blk_mq_start_stopped_hw_queues(q, true);
+}
+
 static void dm_done(struct request *clone, int error, bool mapped)
 {
         int r = error;
@@ -1206,13 +1246,20 @@ static void dm_done(struct request *clone, int error, bool mapped)
 static void dm_softirq_done(struct request *rq)
 {
         bool mapped = true;
-        struct dm_rq_target_io *tio = rq->special;
+        struct dm_rq_target_io *tio = tio_from_request(rq);
         struct request *clone = tio->clone;
+        int rw;
 
         if (!clone) {
-                blk_end_request_all(rq, tio->error);
-                rq_completed(tio->md, rq_data_dir(rq), false);
-                free_rq_tio(tio);
+                rw = rq_data_dir(rq);
+                if (!rq->q->mq_ops) {
+                        blk_end_request_all(rq, tio->error);
+                        rq_completed(tio->md, rw, false);
+                        free_rq_tio(tio);
+                } else {
+                        blk_mq_end_request(rq, tio->error);
+                        rq_completed(tio->md, rw, false);
+                }
                 return;
         }
 
@@ -1228,7 +1275,7 @@ static void dm_softirq_done(struct request *rq)
  */
 static void dm_complete_request(struct request *rq, int error)
 {
-        struct dm_rq_target_io *tio = rq->special;
+        struct dm_rq_target_io *tio = tio_from_request(rq);
 
         tio->error = error;
         blk_complete_request(rq);
@@ -1247,7 +1294,7 @@ static void dm_kill_unmapped_request(struct request *rq, int error)
 }
 
 /*
- * Called with the clone's queue lock held
+ * Called with the clone's queue lock held (for non-blk-mq)
  */
 static void end_clone_request(struct request *clone, int error)
 {
@@ -1808,6 +1855,18 @@ static struct request *clone_rq(struct request *rq, struct mapped_device *md,
 
 static void map_tio_request(struct kthread_work *work);
 
+static void init_tio(struct dm_rq_target_io *tio, struct request *rq,
+                     struct mapped_device *md)
+{
+        tio->md = md;
+        tio->ti = NULL;
+        tio->clone = NULL;
+        tio->orig = rq;
+        tio->error = 0;
+        memset(&tio->info, 0, sizeof(tio->info));
+        init_kthread_work(&tio->work, map_tio_request);
+}
+
 static struct dm_rq_target_io *prep_tio(struct request *rq,
                                         struct mapped_device *md, gfp_t gfp_mask)
 {
@@ -1819,13 +1878,7 @@ static struct dm_rq_target_io *prep_tio(struct request *rq,
         if (!tio)
                 return NULL;
 
-        tio->md = md;
-        tio->ti = NULL;
-        tio->clone = NULL;
-        tio->orig = rq;
-        tio->error = 0;
-        memset(&tio->info, 0, sizeof(tio->info));
-        init_kthread_work(&tio->work, map_tio_request);
+        init_tio(tio, rq, md);
 
         table = dm_get_live_table(md, &srcu_idx);
         if (!dm_table_mq_request_based(table)) {
@@ -1869,11 +1922,11 @@ static int dm_prep_fn(struct request_queue *q, struct request *rq)
  * DM_MAPIO_REQUEUE : the original request needs to be requeued
  * < 0              : the request was completed due to failure
  */
-static int map_request(struct dm_target *ti, struct request *rq,
+static int map_request(struct dm_rq_target_io *tio, struct request *rq,
                        struct mapped_device *md)
 {
         int r;
-        struct dm_rq_target_io *tio = rq->special;
+        struct dm_target *ti = tio->ti;
         struct request *clone = NULL;
 
         if (tio->clone) {
@@ -1888,7 +1941,7 @@ static int map_request(struct dm_target *ti, struct request *rq,
                 }
                 if (IS_ERR(clone))
                         return DM_MAPIO_REQUEUE;
-                if (setup_clone(clone, rq, tio, GFP_KERNEL)) {
+                if (setup_clone(clone, rq, tio, GFP_NOIO)) {
                         /* -ENOMEM */
                         ti->type->release_clone_rq(clone);
                         return DM_MAPIO_REQUEUE;
@@ -1929,13 +1982,16 @@ static void map_tio_request(struct kthread_work *work)
         struct request *rq = tio->orig;
         struct mapped_device *md = tio->md;
 
-        if (map_request(tio->ti, rq, md) == DM_MAPIO_REQUEUE)
+        if (map_request(tio, rq, md) == DM_MAPIO_REQUEUE)
                 dm_requeue_unmapped_original_request(md, rq);
 }
 
 static void dm_start_request(struct mapped_device *md, struct request *orig)
 {
-        blk_start_request(orig);
+        if (!orig->q->mq_ops)
+                blk_start_request(orig);
+        else
+                blk_mq_start_request(orig);
         atomic_inc(&md->pending[rq_data_dir(orig)]);
 
         if (md->seq_rq_merge_deadline_usecs) {
@@ -2045,7 +2101,7 @@ static void dm_request_fn(struct request_queue *q)
 
                 dm_start_request(md, rq);
 
-                tio = rq->special;
+                tio = tio_from_request(rq);
                 /* Establish tio->ti before queuing work (map_tio_request) */
                 tio->ti = ti;
                 queue_kthread_work(&md->kworker, &tio->work);
@@ -2142,7 +2198,7 @@ static void dm_init_md_queue(struct mapped_device *md)
 {
         /*
          * Request-based dm devices cannot be stacked on top of bio-based dm
-         * devices.  The type of this dm device has not been decided yet.
+         * devices.  The type of this dm device may not have been decided yet.
          * The type is decided at the first table loading time.
          * To prevent problematic device stacking, clear the queue flag
          * for request stacking support until then.
@@ -2150,7 +2206,15 @@ static void dm_init_md_queue(struct mapped_device *md)
          * This queue is new, so no concurrency on the queue_flags.
          */
         queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
+}
+
+static void dm_init_old_md_queue(struct mapped_device *md)
+{
+        dm_init_md_queue(md);
 
+        /*
+         * Initialize aspects of queue that aren't relevant for blk-mq
+         */
         md->queue->queuedata = md;
         md->queue->backing_dev_info.congested_fn = dm_any_congested;
         md->queue->backing_dev_info.congested_data = md;
@@ -2273,6 +2337,7 @@ static void unlock_fs(struct mapped_device *md);
 static void free_dev(struct mapped_device *md)
 {
         int minor = MINOR(disk_devt(md->disk));
+        bool using_blk_mq = !!md->queue->mq_ops;
 
         unlock_fs(md);
         destroy_workqueue(md->wq);
@@ -2298,6 +2363,8 @@ static void free_dev(struct mapped_device *md)
         del_gendisk(md->disk);
         put_disk(md->disk);
         blk_cleanup_queue(md->queue);
+        if (using_blk_mq)
+                blk_mq_free_tag_set(&md->tag_set);
         bdput(md->bdev);
         free_minor(minor);
 
@@ -2457,7 +2524,7 @@ static struct dm_table *__bind(struct mapped_device *md, struct dm_table *t,
          * This must be done before setting the queue restrictions,
          * because request-based dm may be run just after the setting.
          */
-        if (dm_table_request_based(t) && !blk_queue_stopped(q))
+        if (dm_table_request_based(t))
                 stop_queue(q);
 
         __bind_mempools(md, t);
@@ -2539,14 +2606,6 @@ unsigned dm_get_md_type(struct mapped_device *md)
         return md->type;
 }
 
-static bool dm_md_type_request_based(struct mapped_device *md)
-{
-        unsigned table_type = dm_get_md_type(md);
-
-        return (table_type == DM_TYPE_REQUEST_BASED ||
-                table_type == DM_TYPE_MQ_REQUEST_BASED);
-}
-
 struct target_type *dm_get_immutable_target_type(struct mapped_device *md)
 {
         return md->immutable_target_type;
@@ -2563,6 +2622,14 @@ struct queue_limits *dm_get_queue_limits(struct mapped_device *md)
 }
 EXPORT_SYMBOL_GPL(dm_get_queue_limits);
 
+static void init_rq_based_worker_thread(struct mapped_device *md)
+{
+        /* Initialize the request-based DM worker thread */
+        init_kthread_worker(&md->kworker);
+        md->kworker_task = kthread_run(kthread_worker_fn, &md->kworker,
+                                       "kdmwork-%s", dm_device_name(md));
+}
+
 /*
  * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
  */
@@ -2571,29 +2638,131 @@ static int dm_init_request_based_queue(struct mapped_device *md)
         struct request_queue *q = NULL;
 
         if (md->queue->elevator)
-                return 1;
+                return 0;
 
         /* Fully initialize the queue */
         q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
         if (!q)
-                return 0;
+                return -EINVAL;
 
         /* disable dm_request_fn's merge heuristic by default */
         md->seq_rq_merge_deadline_usecs = 0;
 
         md->queue = q;
-        dm_init_md_queue(md);
+        dm_init_old_md_queue(md);
         blk_queue_softirq_done(md->queue, dm_softirq_done);
         blk_queue_prep_rq(md->queue, dm_prep_fn);
 
-        /* Also initialize the request-based DM worker thread */
-        init_kthread_worker(&md->kworker);
-        md->kworker_task = kthread_run(kthread_worker_fn, &md->kworker,
-                                       "kdmwork-%s", dm_device_name(md));
+        init_rq_based_worker_thread(md);
 
         elv_register_queue(md->queue);
 
-        return 1;
+        return 0;
+}
+
+static int dm_mq_init_request(void *data, struct request *rq,
+                              unsigned int hctx_idx, unsigned int request_idx,
+                              unsigned int numa_node)
+{
+        struct mapped_device *md = data;
+        struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);
+
+        /*
+         * Must initialize md member of tio, otherwise it won't
+         * be available in dm_mq_queue_rq.
+         */
+        tio->md = md;
+
+        return 0;
+}
+
+static int dm_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
+                          const struct blk_mq_queue_data *bd)
+{
+        struct request *rq = bd->rq;
+        struct dm_rq_target_io *tio = blk_mq_rq_to_pdu(rq);
+        struct mapped_device *md = tio->md;
+        int srcu_idx;
+        struct dm_table *map = dm_get_live_table(md, &srcu_idx);
+        struct dm_target *ti;
+        sector_t pos;
+
+        /* always use block 0 to find the target for flushes for now */
+        pos = 0;
+        if (!(rq->cmd_flags & REQ_FLUSH))
+                pos = blk_rq_pos(rq);
+
+        ti = dm_table_find_target(map, pos);
+        if (!dm_target_is_valid(ti)) {
+                dm_put_live_table(md, srcu_idx);
+                DMERR_LIMIT("request attempted access beyond the end of device");
+                /*
+                 * Must perform setup, that rq_completed() requires,
+                 * before returning BLK_MQ_RQ_QUEUE_ERROR
+                 */
+                dm_start_request(md, rq);
+                return BLK_MQ_RQ_QUEUE_ERROR;
+        }
+        dm_put_live_table(md, srcu_idx);
+
+        if (ti->type->busy && ti->type->busy(ti))
+                return BLK_MQ_RQ_QUEUE_BUSY;
+
+        dm_start_request(md, rq);
+
+        /* Init tio using md established in .init_request */
+        init_tio(tio, rq, md);
+
+        /* Establish tio->ti before queuing work (map_tio_request) */
+        tio->ti = ti;
+        queue_kthread_work(&md->kworker, &tio->work);
+
+        return BLK_MQ_RQ_QUEUE_OK;
+}
+
+static struct blk_mq_ops dm_mq_ops = {
+        .queue_rq = dm_mq_queue_rq,
+        .map_queue = blk_mq_map_queue,
+        .complete = dm_softirq_done,
+        .init_request = dm_mq_init_request,
+};
+
+static int dm_init_request_based_blk_mq_queue(struct mapped_device *md)
+{
+        struct request_queue *q;
+        int err;
+
+        memset(&md->tag_set, 0, sizeof(md->tag_set));
+        md->tag_set.ops = &dm_mq_ops;
+        md->tag_set.queue_depth = BLKDEV_MAX_RQ;
+        md->tag_set.numa_node = NUMA_NO_NODE;
+        md->tag_set.flags = BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_SG_MERGE;
+        md->tag_set.nr_hw_queues = 1;
+        md->tag_set.cmd_size = sizeof(struct dm_rq_target_io);
+        md->tag_set.driver_data = md;
+
+        err = blk_mq_alloc_tag_set(&md->tag_set);
+        if (err)
+                return err;
+
+        q = blk_mq_init_allocated_queue(&md->tag_set, md->queue);
+        if (IS_ERR(q)) {
+                err = PTR_ERR(q);
+                goto out_tag_set;
+        }
+        md->queue = q;
+        dm_init_md_queue(md);
+
+        /* backfill 'mq' sysfs registration normally done in blk_register_queue */
+        blk_mq_register_disk(md->disk);
+
+        init_rq_based_worker_thread(md);
+
+        return 0;
+
+out_tag_set:
+        blk_mq_free_tag_set(&md->tag_set);
+        return err;
 }
 
 /*
@@ -2601,15 +2770,29 @@ static int dm_init_request_based_queue(struct mapped_device *md)
  */
 int dm_setup_md_queue(struct mapped_device *md)
 {
-        if (dm_md_type_request_based(md)) {
-                if (!dm_init_request_based_queue(md)) {
+        int r;
+        unsigned md_type = dm_get_md_type(md);
+
+        switch (md_type) {
+        case DM_TYPE_REQUEST_BASED:
+                r = dm_init_request_based_queue(md);
+                if (r) {
                         DMWARN("Cannot initialize queue for request-based mapped device");
-                        return -EINVAL;
+                        return r;
                 }
-        } else {
-                /* bio-based specific initialization */
+                break;
+        case DM_TYPE_MQ_REQUEST_BASED:
+                r = dm_init_request_based_blk_mq_queue(md);
+                if (r) {
+                        DMWARN("Cannot initialize queue for request-based blk-mq mapped device");
+                        return r;
+                }
+                break;
+        case DM_TYPE_BIO_BASED:
+                dm_init_old_md_queue(md);
                 blk_queue_make_request(md->queue, dm_make_request);
                 blk_queue_merge_bvec(md->queue, dm_merge_bvec);
+                break;
         }
 
         return 0;
diff --git a/include/uapi/linux/dm-ioctl.h b/include/uapi/linux/dm-ioctl.h
index 889f3a5b7b18..eac8c3641f39 100644
--- a/include/uapi/linux/dm-ioctl.h
+++ b/include/uapi/linux/dm-ioctl.h
@@ -267,9 +267,9 @@ enum {
 #define DM_DEV_SET_GEOMETRY     _IOWR(DM_IOCTL, DM_DEV_SET_GEOMETRY_CMD, struct dm_ioctl)
 
 #define DM_VERSION_MAJOR        4
-#define DM_VERSION_MINOR        30
+#define DM_VERSION_MINOR        31
 #define DM_VERSION_PATCHLEVEL   0
-#define DM_VERSION_EXTRA        "-ioctl (2014-12-22)"
+#define DM_VERSION_EXTRA        "-ioctl (2015-3-12)"
 
 /* Status bits */
 #define DM_READONLY_FLAG        (1 << 0) /* In/Out */