[PATCH 0/5] Initial support for polled IO

[PATCH 0/5] Initial support for polled IO

[Jens Axboe]

Hi,

This is a basic framework for supporting polled IO with the block
layer stack, and added support for sync O_DIRECT IO and the NVMe
driver.

There are a few things missing to truly productize this, but it's
very useful for testing. For now, it's a per-device opt-in feature.
To enable it, you echo 1 to /sys/block/<dev>/queue/io_poll.

Some basic test results:

# dd if=/dev/nvme2n1 of=/dev/null bs=4096 iflag=direct count=200k
[...]
838860800 bytes (839 MB) copied, 3.98791 s, 210 MB/s
# echo 1 > /sys/block/nvme2n1/queue/io_poll
# dd if=/dev/nvme2n1 of=/dev/null bs=4096 iflag=direct count=200k
[...]
838860800 bytes (839 MB) copied, 2.15479 s, 389 MB/s

This is a DRAM backed NVMe device, per IO latencies drop from ~19.5usec
to ~10.5usec.

# dd if=/dev/nvme0n1 of=/dev/null bs=4096 iflag=direct count=200k
[...]
838860800 bytes (839 MB) copied, 5.90349 s, 142 MB/s
# echo 1 > /sys/block/nvme0n1/queue/io_poll
# dd if=/dev/nvme0n1 of=/dev/null bs=4096 iflag=direct count=200k
838860800 bytes (839 MB) copied, 3.15852 s, 266 MB/s

Samsung NVMe device, ~28.8 -> ~15.4 usec

# dd if=/dev/nvme1n1 of=/dev/null bs=4096 iflag=direct count=200k
[...]
838860800 bytes (839 MB) copied, 1.78069 s, 471 MB/s
# echo 1 > /sys/block/nvme1n1/queue/io_poll 
# dd if=/dev/nvme1n1 of=/dev/null bs=4096 iflag=direct count=200k
[...]
838860800 bytes (839 MB) copied, 1.31546 s, 638 MB/s

Intel NVMe device, ~8.7usec -> ~6.4usec.

Three different devices, different but notable wins on all of them.
Contrary to intuition, sometimes the slower devices benefit more, since
the slower completion yields a deeper C-state on the processor.

I'd like to get this framework in so we can more easily experiment
with polling. I've got another branch, mq-stats, that wires up a
scalable device IO completion stats collection. We could potentially
use that for enabling smart decisions about when to poll and for how
long. We'll also work on enabling libaio support for this.

Thanks, Jens

[PATCH 1/5] block: change ->make_request_fn() and users to return a queue cookie

[Jens Axboe]

No functional changes in this patch, but it prepares us for returning
a more useful cookie related to the IO that was queued up.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 arch/m68k/emu/nfblock.c                     |  3 ++-
 arch/powerpc/sysdev/axonram.c               |  5 +++--
 arch/xtensa/platforms/iss/simdisk.c         |  3 ++-
 block/blk-core.c                            | 26 ++++++++++++++++----------
 block/blk-mq.c                              | 26 ++++++++++++++------------
 drivers/block/brd.c                         |  5 +++--
 drivers/block/drbd/drbd_int.h               |  2 +-
 drivers/block/drbd/drbd_req.c               |  3 ++-
 drivers/block/null_blk.c                    |  3 ++-
 drivers/block/pktcdvd.c                     |  9 ++++-----
 drivers/block/ps3vram.c                     |  6 ++++--
 drivers/block/rsxx/dev.c                    |  5 +++--
 drivers/block/umem.c                        |  4 ++--
 drivers/block/zram/zram_drv.c               |  5 +++--
 drivers/lightnvm/rrpc.c                     |  9 +++++----
 drivers/md/bcache/request.c                 | 11 ++++++++---
 drivers/md/dm.c                             |  6 +++---
 drivers/md/md.c                             |  8 +++++---
 drivers/nvdimm/blk.c                        |  3 ++-
 drivers/nvdimm/btt.c                        |  3 ++-
 drivers/nvdimm/pmem.c                       |  3 ++-
 drivers/s390/block/dcssblk.c                |  8 +++++---
 drivers/s390/block/xpram.c                  |  5 +++--
 drivers/staging/lustre/lustre/llite/lloop.c |  5 +++--
 include/linux/blk_types.h                   | 24 ++++++++++++++++++++++++
 include/linux/blkdev.h                      |  4 ++--
 include/linux/fs.h                          |  2 +-
 include/linux/lightnvm.h                    |  2 +-
 28 files changed, 127 insertions(+), 71 deletions(-)

diff --git a/arch/m68k/emu/nfblock.c b/arch/m68k/emu/nfblock.c
index f2a00c591bf7..e9110b9b8bcd 100644
--- a/arch/m68k/emu/nfblock.c
+++ b/arch/m68k/emu/nfblock.c
@@ -59,7 +59,7 @@ struct nfhd_device {
 	struct gendisk *disk;
 };
 
-static void nfhd_make_request(struct request_queue *queue, struct bio *bio)
+static blk_qc_t nfhd_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct nfhd_device *dev = queue->queuedata;
 	struct bio_vec bvec;
@@ -77,6 +77,7 @@ static void nfhd_make_request(struct request_queue *queue, struct bio *bio)
 		sec += len;
 	}
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int nfhd_getgeo(struct block_device *bdev, struct hd_geometry *geo)
diff --git a/arch/powerpc/sysdev/axonram.c b/arch/powerpc/sysdev/axonram.c
index d2b79bc336c1..7a399b4d60a0 100644
--- a/arch/powerpc/sysdev/axonram.c
+++ b/arch/powerpc/sysdev/axonram.c
@@ -103,7 +103,7 @@ axon_ram_irq_handler(int irq, void *dev)
  * axon_ram_make_request - make_request() method for block device
  * @queue, @bio: see blk_queue_make_request()
  */
-static void
+static blk_qc_t
 axon_ram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct axon_ram_bank *bank = bio->bi_bdev->bd_disk->private_data;
@@ -120,7 +120,7 @@ axon_ram_make_request(struct request_queue *queue, struct bio *bio)
 	bio_for_each_segment(vec, bio, iter) {
 		if (unlikely(phys_mem + vec.bv_len > phys_end)) {
 			bio_io_error(bio);
-			return;
+			return BLK_QC_T_NONE;
 		}
 
 		user_mem = page_address(vec.bv_page) + vec.bv_offset;
@@ -133,6 +133,7 @@ axon_ram_make_request(struct request_queue *queue, struct bio *bio)
 		transfered += vec.bv_len;
 	}
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 /**
diff --git a/arch/xtensa/platforms/iss/simdisk.c b/arch/xtensa/platforms/iss/simdisk.c
index fa84ca990caa..3c3ace2c46b6 100644
--- a/arch/xtensa/platforms/iss/simdisk.c
+++ b/arch/xtensa/platforms/iss/simdisk.c
@@ -101,7 +101,7 @@ static void simdisk_transfer(struct simdisk *dev, unsigned long sector,
 	spin_unlock(&dev->lock);
 }
 
-static void simdisk_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t simdisk_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct simdisk *dev = q->queuedata;
 	struct bio_vec bvec;
@@ -119,6 +119,7 @@ static void simdisk_make_request(struct request_queue *q, struct bio *bio)
 	}
 
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int simdisk_open(struct block_device *bdev, fmode_t mode)
diff --git a/block/blk-core.c b/block/blk-core.c
index 89eec7965870..e93df6d386a0 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -809,7 +809,7 @@ blk_init_queue_node(request_fn_proc *rfn, spinlock_t *lock, int node_id)
 }
 EXPORT_SYMBOL(blk_init_queue_node);
 
-static void blk_queue_bio(struct request_queue *q, struct bio *bio);
+static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio);
 
 struct request_queue *
 blk_init_allocated_queue(struct request_queue *q, request_fn_proc *rfn,
@@ -1678,7 +1678,7 @@ void init_request_from_bio(struct request *req, struct bio *bio)
 	blk_rq_bio_prep(req->q, req, bio);
 }
 
-static void blk_queue_bio(struct request_queue *q, struct bio *bio)
+static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio)
 {
 	const bool sync = !!(bio->bi_rw & REQ_SYNC);
 	struct blk_plug *plug;
@@ -1698,7 +1698,7 @@ static void blk_queue_bio(struct request_queue *q, struct bio *bio)
 	if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
 		bio->bi_error = -EIO;
 		bio_endio(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
@@ -1713,7 +1713,7 @@ static void blk_queue_bio(struct request_queue *q, struct bio *bio)
 	 */
 	if (!blk_queue_nomerges(q)) {
 		if (blk_attempt_plug_merge(q, bio, &request_count, NULL))
-			return;
+			return BLK_QC_T_NONE;
 	} else
 		request_count = blk_plug_queued_count(q);
 
@@ -1791,6 +1791,8 @@ get_rq:
 out_unlock:
 		spin_unlock_irq(q->queue_lock);
 	}
+
+	return BLK_QC_T_NONE;
 }
 
 /*
@@ -1996,12 +1998,13 @@ end_io:
  * a lower device by calling into generic_make_request recursively, which
  * means the bio should NOT be touched after the call to ->make_request_fn.
  */
-void generic_make_request(struct bio *bio)
+blk_qc_t generic_make_request(struct bio *bio)
 {
 	struct bio_list bio_list_on_stack;
+	blk_qc_t ret = BLK_QC_T_NONE;
 
 	if (!generic_make_request_checks(bio))
-		return;
+		goto out;
 
 	/*
 	 * We only want one ->make_request_fn to be active at a time, else
@@ -2015,7 +2018,7 @@ void generic_make_request(struct bio *bio)
 	 */
 	if (current->bio_list) {
 		bio_list_add(current->bio_list, bio);
-		return;
+		goto out;
 	}
 
 	/* following loop may be a bit non-obvious, and so deserves some
@@ -2040,7 +2043,7 @@ void generic_make_request(struct bio *bio)
 
 		if (likely(blk_queue_enter(q, __GFP_WAIT) == 0)) {
 
-			q->make_request_fn(q, bio);
+			ret = q->make_request_fn(q, bio);
 
 			blk_queue_exit(q);
 
@@ -2053,6 +2056,9 @@ void generic_make_request(struct bio *bio)
 		}
 	} while (bio);
 	current->bio_list = NULL; /* deactivate */
+
+out:
+	return ret;
 }
 EXPORT_SYMBOL(generic_make_request);
 
@@ -2066,7 +2072,7 @@ EXPORT_SYMBOL(generic_make_request);
  * interfaces; @bio must be presetup and ready for I/O.
  *
  */
-void submit_bio(int rw, struct bio *bio)
+blk_qc_t submit_bio(int rw, struct bio *bio)
 {
 	bio->bi_rw |= rw;
 
@@ -2100,7 +2106,7 @@ void submit_bio(int rw, struct bio *bio)
 		}
 	}
 
-	generic_make_request(bio);
+	return generic_make_request(bio);
 }
 EXPORT_SYMBOL(submit_bio);
 
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 1c27b3eaef64..65f43bd696a0 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1235,7 +1235,7 @@ static int blk_mq_direct_issue_request(struct request *rq)
  * but will attempt to bypass the hctx queueing if we can go straight to
  * hardware for SYNC IO.
  */
-static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 {
 	const int is_sync = rw_is_sync(bio->bi_rw);
 	const int is_flush_fua = bio->bi_rw & (REQ_FLUSH | REQ_FUA);
@@ -1249,7 +1249,7 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
 
 	if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
 		bio_io_error(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	blk_queue_split(q, &bio, q->bio_split);
@@ -1257,13 +1257,13 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	if (!is_flush_fua && !blk_queue_nomerges(q)) {
 		if (blk_attempt_plug_merge(q, bio, &request_count,
 					   &same_queue_rq))
-			return;
+			return BLK_QC_T_NONE;
 	} else
 		request_count = blk_plug_queued_count(q);
 
 	rq = blk_mq_map_request(q, bio, &data);
 	if (unlikely(!rq))
-		return;
+		return BLK_QC_T_NONE;
 
 	if (unlikely(is_flush_fua)) {
 		blk_mq_bio_to_request(rq, bio);
@@ -1302,11 +1302,11 @@ static void blk_mq_make_request(struct request_queue *q, struct bio *bio)
 			old_rq = rq;
 		blk_mq_put_ctx(data.ctx);
 		if (!old_rq)
-			return;
+			return BLK_QC_T_NONE;
 		if (!blk_mq_direct_issue_request(old_rq))
-			return;
+			return BLK_QC_T_NONE;
 		blk_mq_insert_request(old_rq, false, true, true);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
@@ -1320,13 +1320,14 @@ run_queue:
 		blk_mq_run_hw_queue(data.hctx, !is_sync || is_flush_fua);
 	}
 	blk_mq_put_ctx(data.ctx);
+	return BLK_QC_T_NONE;
 }
 
 /*
  * Single hardware queue variant. This will attempt to use any per-process
  * plug for merging and IO deferral.
  */
-static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 {
 	const int is_sync = rw_is_sync(bio->bi_rw);
 	const int is_flush_fua = bio->bi_rw & (REQ_FLUSH | REQ_FUA);
@@ -1339,18 +1340,18 @@ static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
 
 	if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
 		bio_io_error(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	blk_queue_split(q, &bio, q->bio_split);
 
 	if (!is_flush_fua && !blk_queue_nomerges(q) &&
 	    blk_attempt_plug_merge(q, bio, &request_count, NULL))
-		return;
+		return BLK_QC_T_NONE;
 
 	rq = blk_mq_map_request(q, bio, &data);
 	if (unlikely(!rq))
-		return;
+		return BLK_QC_T_NONE;
 
 	if (unlikely(is_flush_fua)) {
 		blk_mq_bio_to_request(rq, bio);
@@ -1374,7 +1375,7 @@ static void blk_sq_make_request(struct request_queue *q, struct bio *bio)
 		}
 		list_add_tail(&rq->queuelist, &plug->mq_list);
 		blk_mq_put_ctx(data.ctx);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
@@ -1389,6 +1390,7 @@ run_queue:
 	}
 
 	blk_mq_put_ctx(data.ctx);
+	return BLK_QC_T_NONE;
 }
 
 /*
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index b9794aeeb878..c9f9c30d6467 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -323,7 +323,7 @@ out:
 	return err;
 }
 
-static void brd_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t brd_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct block_device *bdev = bio->bi_bdev;
 	struct brd_device *brd = bdev->bd_disk->private_data;
@@ -358,9 +358,10 @@ static void brd_make_request(struct request_queue *q, struct bio *bio)
 
 out:
 	bio_endio(bio);
-	return;
+	return BLK_QC_T_NONE;
 io_error:
 	bio_io_error(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int brd_rw_page(struct block_device *bdev, sector_t sector,
diff --git a/drivers/block/drbd/drbd_int.h b/drivers/block/drbd/drbd_int.h
index 015c6e91b756..e66d453a5f2b 100644
--- a/drivers/block/drbd/drbd_int.h
+++ b/drivers/block/drbd/drbd_int.h
@@ -1448,7 +1448,7 @@ extern int proc_details;
 /* drbd_req */
 extern void do_submit(struct work_struct *ws);
 extern void __drbd_make_request(struct drbd_device *, struct bio *, unsigned long);
-extern void drbd_make_request(struct request_queue *q, struct bio *bio);
+extern blk_qc_t drbd_make_request(struct request_queue *q, struct bio *bio);
 extern int drbd_read_remote(struct drbd_device *device, struct drbd_request *req);
 extern int is_valid_ar_handle(struct drbd_request *, sector_t);
 
diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index 211592682169..3ae2c0086563 100644
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -1494,7 +1494,7 @@ void do_submit(struct work_struct *ws)
 	}
 }
 
-void drbd_make_request(struct request_queue *q, struct bio *bio)
+blk_qc_t drbd_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct drbd_device *device = (struct drbd_device *) q->queuedata;
 	unsigned long start_jif;
@@ -1510,6 +1510,7 @@ void drbd_make_request(struct request_queue *q, struct bio *bio)
 
 	inc_ap_bio(device);
 	__drbd_make_request(device, bio, start_jif);
+	return BLK_QC_T_NONE;
 }
 
 void request_timer_fn(unsigned long data)
diff --git a/drivers/block/null_blk.c b/drivers/block/null_blk.c
index 1c9e4fe5aa44..6255d1c4bba4 100644
--- a/drivers/block/null_blk.c
+++ b/drivers/block/null_blk.c
@@ -321,7 +321,7 @@ static struct nullb_queue *nullb_to_queue(struct nullb *nullb)
 	return &nullb->queues[index];
 }
 
-static void null_queue_bio(struct request_queue *q, struct bio *bio)
+static blk_qc_t null_queue_bio(struct request_queue *q, struct bio *bio)
 {
 	struct nullb *nullb = q->queuedata;
 	struct nullb_queue *nq = nullb_to_queue(nullb);
@@ -331,6 +331,7 @@ static void null_queue_bio(struct request_queue *q, struct bio *bio)
 	cmd->bio = bio;
 
 	null_handle_cmd(cmd);
+	return BLK_QC_T_NONE;
 }
 
 static int null_rq_prep_fn(struct request_queue *q, struct request *req)
diff --git a/drivers/block/pktcdvd.c b/drivers/block/pktcdvd.c
index 7be2375db7f2..a7f4abcedee1 100644
--- a/drivers/block/pktcdvd.c
+++ b/drivers/block/pktcdvd.c
@@ -2441,7 +2441,7 @@ static void pkt_make_request_write(struct request_queue *q, struct bio *bio)
 	}
 }
 
-static void pkt_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t pkt_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct pktcdvd_device *pd;
 	char b[BDEVNAME_SIZE];
@@ -2467,7 +2467,7 @@ static void pkt_make_request(struct request_queue *q, struct bio *bio)
 	 */
 	if (bio_data_dir(bio) == READ) {
 		pkt_make_request_read(pd, bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	if (!test_bit(PACKET_WRITABLE, &pd->flags)) {
@@ -2499,13 +2499,12 @@ static void pkt_make_request(struct request_queue *q, struct bio *bio)
 		pkt_make_request_write(q, split);
 	} while (split != bio);
 
-	return;
+	return BLK_QC_T_NONE;
 end_io:
 	bio_io_error(bio);
+	return BLK_QC_T_NONE;
 }
 
-
-
 static void pkt_init_queue(struct pktcdvd_device *pd)
 {
 	struct request_queue *q = pd->disk->queue;
diff --git a/drivers/block/ps3vram.c b/drivers/block/ps3vram.c
index d89fcac59515..56847fcda086 100644
--- a/drivers/block/ps3vram.c
+++ b/drivers/block/ps3vram.c
@@ -598,7 +598,7 @@ out:
 	return next;
 }
 
-static void ps3vram_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t ps3vram_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct ps3_system_bus_device *dev = q->queuedata;
 	struct ps3vram_priv *priv = ps3_system_bus_get_drvdata(dev);
@@ -614,11 +614,13 @@ static void ps3vram_make_request(struct request_queue *q, struct bio *bio)
 	spin_unlock_irq(&priv->lock);
 
 	if (busy)
-		return;
+		return BLK_QC_T_NONE;
 
 	do {
 		bio = ps3vram_do_bio(dev, bio);
 	} while (bio);
+
+	return BLK_QC_T_NONE;
 }
 
 static int ps3vram_probe(struct ps3_system_bus_device *dev)
diff --git a/drivers/block/rsxx/dev.c b/drivers/block/rsxx/dev.c
index 3163e4cdc2cc..e1b8b7061d2f 100644
--- a/drivers/block/rsxx/dev.c
+++ b/drivers/block/rsxx/dev.c
@@ -145,7 +145,7 @@ static void bio_dma_done_cb(struct rsxx_cardinfo *card,
 	}
 }
 
-static void rsxx_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t rsxx_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct rsxx_cardinfo *card = q->queuedata;
 	struct rsxx_bio_meta *bio_meta;
@@ -199,7 +199,7 @@ static void rsxx_make_request(struct request_queue *q, struct bio *bio)
 	if (st)
 		goto queue_err;
 
-	return;
+	return BLK_QC_T_NONE;
 
 queue_err:
 	kmem_cache_free(bio_meta_pool, bio_meta);
@@ -207,6 +207,7 @@ req_err:
 	if (st)
 		bio->bi_error = st;
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 /*----------------- Device Setup -------------------*/
diff --git a/drivers/block/umem.c b/drivers/block/umem.c
index 04d65790a886..7939b9f87441 100644
--- a/drivers/block/umem.c
+++ b/drivers/block/umem.c
@@ -524,7 +524,7 @@ static int mm_check_plugged(struct cardinfo *card)
 	return !!blk_check_plugged(mm_unplug, card, sizeof(struct blk_plug_cb));
 }
 
-static void mm_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t mm_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct cardinfo *card = q->queuedata;
 	pr_debug("mm_make_request %llu %u\n",
@@ -541,7 +541,7 @@ static void mm_make_request(struct request_queue *q, struct bio *bio)
 		activate(card);
 	spin_unlock_irq(&card->lock);
 
-	return;
+	return BLK_QC_T_NONE;
 }
 
 static irqreturn_t mm_interrupt(int irq, void *__card)
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9fa15bb9d118..4c99b6ba8681 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -894,7 +894,7 @@ out:
 /*
  * Handler function for all zram I/O requests.
  */
-static void zram_make_request(struct request_queue *queue, struct bio *bio)
+static blk_qc_t zram_make_request(struct request_queue *queue, struct bio *bio)
 {
 	struct zram *zram = queue->queuedata;
 
@@ -911,11 +911,12 @@ static void zram_make_request(struct request_queue *queue, struct bio *bio)
 
 	__zram_make_request(zram, bio);
 	zram_meta_put(zram);
-	return;
+	return BLK_QC_T_NONE;
 put_zram:
 	zram_meta_put(zram);
 error:
 	bio_io_error(bio);
+	return BLK_QC_T_NONE;
 }
 
 static void zram_slot_free_notify(struct block_device *bdev,
diff --git a/drivers/lightnvm/rrpc.c b/drivers/lightnvm/rrpc.c
index 64a888a5e9b3..7ba64c87ba1c 100644
--- a/drivers/lightnvm/rrpc.c
+++ b/drivers/lightnvm/rrpc.c
@@ -803,7 +803,7 @@ static int rrpc_submit_io(struct rrpc *rrpc, struct bio *bio,
 	return NVM_IO_OK;
 }
 
-static void rrpc_make_rq(struct request_queue *q, struct bio *bio)
+static blk_qc_t rrpc_make_rq(struct request_queue *q, struct bio *bio)
 {
 	struct rrpc *rrpc = q->queuedata;
 	struct nvm_rq *rqd;
@@ -811,21 +811,21 @@ static void rrpc_make_rq(struct request_queue *q, struct bio *bio)
 
 	if (bio->bi_rw & REQ_DISCARD) {
 		rrpc_discard(rrpc, bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	rqd = mempool_alloc(rrpc->rq_pool, GFP_KERNEL);
 	if (!rqd) {
 		pr_err_ratelimited("rrpc: not able to queue bio.");
 		bio_io_error(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 	memset(rqd, 0, sizeof(struct nvm_rq));
 
 	err = rrpc_submit_io(rrpc, bio, rqd, NVM_IOTYPE_NONE);
 	switch (err) {
 	case NVM_IO_OK:
-		return;
+		return BLK_QC_T_NONE;
 	case NVM_IO_ERR:
 		bio_io_error(bio);
 		break;
@@ -841,6 +841,7 @@ static void rrpc_make_rq(struct request_queue *q, struct bio *bio)
 	}
 
 	mempool_free(rqd, rrpc->rq_pool);
+	return BLK_QC_T_NONE;
 }
 
 static void rrpc_requeue(struct work_struct *work)
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 8e9877b04637..25fa8445bb24 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -958,7 +958,8 @@ static void cached_dev_nodata(struct closure *cl)
 
 /* Cached devices - read & write stuff */
 
-static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t cached_dev_make_request(struct request_queue *q,
+					struct bio *bio)
 {
 	struct search *s;
 	struct bcache_device *d = bio->bi_bdev->bd_disk->private_data;
@@ -997,6 +998,8 @@ static void cached_dev_make_request(struct request_queue *q, struct bio *bio)
 		else
 			generic_make_request(bio);
 	}
+
+	return BLK_QC_T_NONE;
 }
 
 static int cached_dev_ioctl(struct bcache_device *d, fmode_t mode,
@@ -1070,7 +1073,8 @@ static void flash_dev_nodata(struct closure *cl)
 	continue_at(cl, search_free, NULL);
 }
 
-static void flash_dev_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t flash_dev_make_request(struct request_queue *q,
+					     struct bio *bio)
 {
 	struct search *s;
 	struct closure *cl;
@@ -1093,7 +1097,7 @@ static void flash_dev_make_request(struct request_queue *q, struct bio *bio)
 		continue_at_nobarrier(&s->cl,
 				      flash_dev_nodata,
 				      bcache_wq);
-		return;
+		return BLK_QC_T_NONE;
 	} else if (rw) {
 		bch_keybuf_check_overlapping(&s->iop.c->moving_gc_keys,
 					&KEY(d->id, bio->bi_iter.bi_sector, 0),
@@ -1109,6 +1113,7 @@ static void flash_dev_make_request(struct request_queue *q, struct bio *bio)
 	}
 
 	continue_at(cl, search_free, NULL);
+	return BLK_QC_T_NONE;
 }
 
 static int flash_dev_ioctl(struct bcache_device *d, fmode_t mode,
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 32440ad5f684..6e15f3565892 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1755,7 +1755,7 @@ static void __split_and_process_bio(struct mapped_device *md,
  * The request function that just remaps the bio built up by
  * dm_merge_bvec.
  */
-static void dm_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio)
 {
 	int rw = bio_data_dir(bio);
 	struct mapped_device *md = q->queuedata;
@@ -1774,12 +1774,12 @@ static void dm_make_request(struct request_queue *q, struct bio *bio)
 			queue_io(md, bio);
 		else
 			bio_io_error(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 
 	__split_and_process_bio(md, map, bio);
 	dm_put_live_table(md, srcu_idx);
-	return;
+	return BLK_QC_T_NONE;
 }
 
 int dm_request_based(struct mapped_device *md)
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 3f9a514b5b9d..807095f4c793 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -250,7 +250,7 @@ static DEFINE_SPINLOCK(all_mddevs_lock);
  * call has finished, the bio has been linked into some internal structure
  * and so is visible to ->quiesce(), so we don't need the refcount any more.
  */
-static void md_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t md_make_request(struct request_queue *q, struct bio *bio)
 {
 	const int rw = bio_data_dir(bio);
 	struct mddev *mddev = q->queuedata;
@@ -262,13 +262,13 @@ static void md_make_request(struct request_queue *q, struct bio *bio)
 	if (mddev == NULL || mddev->pers == NULL
 	    || !mddev->ready) {
 		bio_io_error(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 	if (mddev->ro == 1 && unlikely(rw == WRITE)) {
 		if (bio_sectors(bio) != 0)
 			bio->bi_error = -EROFS;
 		bio_endio(bio);
-		return;
+		return BLK_QC_T_NONE;
 	}
 	smp_rmb(); /* Ensure implications of  'active' are visible */
 	rcu_read_lock();
@@ -302,6 +302,8 @@ static void md_make_request(struct request_queue *q, struct bio *bio)
 
 	if (atomic_dec_and_test(&mddev->active_io) && mddev->suspended)
 		wake_up(&mddev->sb_wait);
+
+	return BLK_QC_T_NONE;
 }
 
 /* mddev_suspend makes sure no new requests are submitted
diff --git a/drivers/nvdimm/blk.c b/drivers/nvdimm/blk.c
index 0df77cb07df6..91a336ea8c4f 100644
--- a/drivers/nvdimm/blk.c
+++ b/drivers/nvdimm/blk.c
@@ -161,7 +161,7 @@ static int nd_blk_do_bvec(struct nd_blk_device *blk_dev,
 	return err;
 }
 
-static void nd_blk_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t nd_blk_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct block_device *bdev = bio->bi_bdev;
 	struct gendisk *disk = bdev->bd_disk;
@@ -208,6 +208,7 @@ static void nd_blk_make_request(struct request_queue *q, struct bio *bio)
 
  out:
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int nd_blk_rw_bytes(struct nd_namespace_common *ndns,
diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index eae93ab8ffcd..efb2c1ceef98 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -1150,7 +1150,7 @@ static int btt_do_bvec(struct btt *btt, struct bio_integrity_payload *bip,
 	return ret;
 }
 
-static void btt_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t btt_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct bio_integrity_payload *bip = bio_integrity(bio);
 	struct btt *btt = q->queuedata;
@@ -1198,6 +1198,7 @@ static void btt_make_request(struct request_queue *q, struct bio *bio)
 
 out:
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int btt_rw_page(struct block_device *bdev, sector_t sector,
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 0ba6a978f227..3963b7533b65 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -64,7 +64,7 @@ static void pmem_do_bvec(struct pmem_device *pmem, struct page *page,
 	kunmap_atomic(mem);
 }
 
-static void pmem_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t pmem_make_request(struct request_queue *q, struct bio *bio)
 {
 	bool do_acct;
 	unsigned long start;
@@ -84,6 +84,7 @@ static void pmem_make_request(struct request_queue *q, struct bio *bio)
 		wmb_pmem();
 
 	bio_endio(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int pmem_rw_page(struct block_device *bdev, sector_t sector,
diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
index 5ed44fe21380..94a8f4ab57bc 100644
--- a/drivers/s390/block/dcssblk.c
+++ b/drivers/s390/block/dcssblk.c
@@ -27,7 +27,8 @@
 
 static int dcssblk_open(struct block_device *bdev, fmode_t mode);
 static void dcssblk_release(struct gendisk *disk, fmode_t mode);
-static void dcssblk_make_request(struct request_queue *q, struct bio *bio);
+static blk_qc_t dcssblk_make_request(struct request_queue *q,
+						struct bio *bio);
 static long dcssblk_direct_access(struct block_device *bdev, sector_t secnum,
 			 void __pmem **kaddr, unsigned long *pfn);
 
@@ -815,7 +816,7 @@ dcssblk_release(struct gendisk *disk, fmode_t mode)
 	up_write(&dcssblk_devices_sem);
 }
 
-static void
+static blk_qc_t
 dcssblk_make_request(struct request_queue *q, struct bio *bio)
 {
 	struct dcssblk_dev_info *dev_info;
@@ -874,9 +875,10 @@ dcssblk_make_request(struct request_queue *q, struct bio *bio)
 		bytes_done += bvec.bv_len;
 	}
 	bio_endio(bio);
-	return;
+	return BLK_QC_T_NONE;
 fail:
 	bio_io_error(bio);
+	return BLK_QC_T_NONE;
 }
 
 static long
diff --git a/drivers/s390/block/xpram.c b/drivers/s390/block/xpram.c
index 02871f1db562..288f59a4147b 100644
--- a/drivers/s390/block/xpram.c
+++ b/drivers/s390/block/xpram.c
@@ -181,7 +181,7 @@ static unsigned long xpram_highest_page_index(void)
 /*
  * Block device make request function.
  */
-static void xpram_make_request(struct request_queue *q, struct bio *bio)
+static blk_qc_t xpram_make_request(struct request_queue *q, struct bio *bio)
 {
 	xpram_device_t *xdev = bio->bi_bdev->bd_disk->private_data;
 	struct bio_vec bvec;
@@ -223,9 +223,10 @@ static void xpram_make_request(struct request_queue *q, struct bio *bio)
 		}
 	}
 	bio_endio(bio);
-	return;
+	return BLK_QC_T_NONE;
 fail:
 	bio_io_error(bio);
+	return BLK_QC_T_NONE;
 }
 
 static int xpram_getgeo(struct block_device *bdev, struct hd_geometry *geo)
diff --git a/drivers/staging/lustre/lustre/llite/lloop.c b/drivers/staging/lustre/lustre/llite/lloop.c
index e6974c36276d..fed50d538a41 100644
--- a/drivers/staging/lustre/lustre/llite/lloop.c
+++ b/drivers/staging/lustre/lustre/llite/lloop.c
@@ -333,7 +333,7 @@ static unsigned int loop_get_bio(struct lloop_device *lo, struct bio **req)
 	return count;
 }
 
-static void loop_make_request(struct request_queue *q, struct bio *old_bio)
+static blk_qc_t loop_make_request(struct request_queue *q, struct bio *old_bio)
 {
 	struct lloop_device *lo = q->queuedata;
 	int rw = bio_rw(old_bio);
@@ -364,9 +364,10 @@ static void loop_make_request(struct request_queue *q, struct bio *old_bio)
 		goto err;
 	}
 	loop_add_bio(lo, old_bio);
-	return;
+	return BLK_QC_T_NONE;
 err:
 	bio_io_error(old_bio);
+	return BLK_QC_T_NONE;
 }
 
 static inline void loop_handle_bio(struct lloop_device *lo, struct bio *bio)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index e8130138f29d..641e5a3ed58c 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -244,4 +244,28 @@ enum rq_flag_bits {
 #define REQ_MQ_INFLIGHT		(1ULL << __REQ_MQ_INFLIGHT)
 #define REQ_NO_TIMEOUT		(1ULL << __REQ_NO_TIMEOUT)
 
+typedef unsigned int blk_qc_t;
+#define BLK_QC_T_NONE	-1U
+#define BLK_QC_T_SHIFT	16
+
+static inline bool blk_qc_t_valid(blk_qc_t cookie)
+{
+	return cookie != BLK_QC_T_NONE;
+}
+
+static inline blk_qc_t blk_tag_to_qc_t(unsigned int tag, unsigned int queue_num)
+{
+	return tag | (queue_num << BLK_QC_T_SHIFT);
+}
+
+static inline unsigned int blk_qc_t_to_queue_num(blk_qc_t cookie)
+{
+	return cookie >> BLK_QC_T_SHIFT;
+}
+
+static inline unsigned int blk_qc_t_to_tag(blk_qc_t cookie)
+{
+	return cookie & 0xffff;
+}
+
 #endif /* __LINUX_BLK_TYPES_H */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d045ca8487af..5ee0f5243025 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -209,7 +209,7 @@ static inline unsigned short req_get_ioprio(struct request *req)
 struct blk_queue_ctx;
 
 typedef void (request_fn_proc) (struct request_queue *q);
-typedef void (make_request_fn) (struct request_queue *q, struct bio *bio);
+typedef blk_qc_t (make_request_fn) (struct request_queue *q, struct bio *bio);
 typedef int (prep_rq_fn) (struct request_queue *, struct request *);
 typedef void (unprep_rq_fn) (struct request_queue *, struct request *);
 
@@ -761,7 +761,7 @@ static inline void rq_flush_dcache_pages(struct request *rq)
 
 extern int blk_register_queue(struct gendisk *disk);
 extern void blk_unregister_queue(struct gendisk *disk);
-extern void generic_make_request(struct bio *bio);
+extern blk_qc_t generic_make_request(struct bio *bio);
 extern void blk_rq_init(struct request_queue *q, struct request *rq);
 extern void blk_put_request(struct request *);
 extern void __blk_put_request(struct request_queue *, struct request *);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 72d8a844c692..bcca36e4bc1e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2625,7 +2625,7 @@ static inline void remove_inode_hash(struct inode *inode)
 extern void inode_sb_list_add(struct inode *inode);
 
 #ifdef CONFIG_BLOCK
-extern void submit_bio(int, struct bio *);
+extern blk_qc_t submit_bio(int, struct bio *);
 extern int bdev_read_only(struct block_device *);
 #endif
 extern int set_blocksize(struct block_device *, int);
diff --git a/include/linux/lightnvm.h b/include/linux/lightnvm.h
index 5ebd70d12f35..69c9057e1ab8 100644
--- a/include/linux/lightnvm.h
+++ b/include/linux/lightnvm.h
@@ -426,7 +426,7 @@ static inline struct ppa_addr block_to_ppa(struct nvm_dev *dev,
 	return ppa;
 }
 
-typedef void (nvm_tgt_make_rq_fn)(struct request_queue *, struct bio *);
+typedef blk_qc_t (nvm_tgt_make_rq_fn)(struct request_queue *, struct bio *);
 typedef sector_t (nvm_tgt_capacity_fn)(void *);
 typedef int (nvm_tgt_end_io_fn)(struct nvm_rq *, int);
 typedef void *(nvm_tgt_init_fn)(struct nvm_dev *, struct gendisk *, int, int);
-- 
2.4.1.168.g1ea28e1

[PATCH 2/5] blk-mq: return tag/queue combo in the make_request_fn handlers

[Jens Axboe]

Return a cookie, blk_qc_t, from the blk-mq make request functions, that
allows a later caller to uniquely identify a specific IO. The cookie
doesn't mean anything to the caller, but the caller can use it to later
pass back to the block layer. The block layer can then identify the
hardware queue and request from that cookie.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/blk-mq.c | 45 ++++++++++++++++++++++++++++-----------------
 1 file changed, 28 insertions(+), 17 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 65f43bd696a0..66f3cf9c436d 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1198,7 +1198,7 @@ static struct request *blk_mq_map_request(struct request_queue *q,
 	return rq;
 }
 
-static int blk_mq_direct_issue_request(struct request *rq)
+static int blk_mq_direct_issue_request(struct request *rq, blk_qc_t *cookie)
 {
 	int ret;
 	struct request_queue *q = rq->q;
@@ -1209,6 +1209,7 @@ static int blk_mq_direct_issue_request(struct request *rq)
 		.list = NULL,
 		.last = 1
 	};
+	blk_qc_t new_cookie = blk_tag_to_qc_t(rq->tag, hctx->queue_num);
 
 	/*
 	 * For OK queue, we are done. For error, kill it. Any other
@@ -1216,18 +1217,21 @@ static int blk_mq_direct_issue_request(struct request *rq)
 	 * would have done
 	 */
 	ret = q->mq_ops->queue_rq(hctx, &bd);
-	if (ret == BLK_MQ_RQ_QUEUE_OK)
+	if (ret == BLK_MQ_RQ_QUEUE_OK) {
+		*cookie = new_cookie;
 		return 0;
-	else {
-		__blk_mq_requeue_request(rq);
+	}
 
-		if (ret == BLK_MQ_RQ_QUEUE_ERROR) {
-			rq->errors = -EIO;
-			blk_mq_end_request(rq, rq->errors);
-			return 0;
-		}
-		return -1;
+	__blk_mq_requeue_request(rq);
+
+	if (ret == BLK_MQ_RQ_QUEUE_ERROR) {
+		*cookie = BLK_QC_T_NONE;
+		rq->errors = -EIO;
+		blk_mq_end_request(rq, rq->errors);
+		return 0;
 	}
+
+	return -1;
 }
 
 /*
@@ -1244,6 +1248,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	unsigned int request_count = 0;
 	struct blk_plug *plug;
 	struct request *same_queue_rq = NULL;
+	blk_qc_t cookie;
 
 	blk_queue_bounce(q, &bio);
 
@@ -1265,6 +1270,8 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 	if (unlikely(!rq))
 		return BLK_QC_T_NONE;
 
+	cookie = blk_tag_to_qc_t(rq->tag, data.hctx->queue_num);
+
 	if (unlikely(is_flush_fua)) {
 		blk_mq_bio_to_request(rq, bio);
 		blk_insert_flush(rq);
@@ -1302,11 +1309,11 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
 			old_rq = rq;
 		blk_mq_put_ctx(data.ctx);
 		if (!old_rq)
-			return BLK_QC_T_NONE;
-		if (!blk_mq_direct_issue_request(old_rq))
-			return BLK_QC_T_NONE;
+			goto done;
+		if (!blk_mq_direct_issue_request(old_rq, &cookie))
+			goto done;
 		blk_mq_insert_request(old_rq, false, true, true);
-		return BLK_QC_T_NONE;
+		goto done;
 	}
 
 	if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
@@ -1320,7 +1327,8 @@ run_queue:
 		blk_mq_run_hw_queue(data.hctx, !is_sync || is_flush_fua);
 	}
 	blk_mq_put_ctx(data.ctx);
-	return BLK_QC_T_NONE;
+done:
+	return cookie;
 }
 
 /*
@@ -1335,6 +1343,7 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 	unsigned int request_count = 0;
 	struct blk_map_ctx data;
 	struct request *rq;
+	blk_qc_t cookie;
 
 	blk_queue_bounce(q, &bio);
 
@@ -1353,6 +1362,8 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 	if (unlikely(!rq))
 		return BLK_QC_T_NONE;
 
+	cookie = blk_tag_to_qc_t(rq->tag, data.hctx->queue_num);
+
 	if (unlikely(is_flush_fua)) {
 		blk_mq_bio_to_request(rq, bio);
 		blk_insert_flush(rq);
@@ -1375,7 +1386,7 @@ static blk_qc_t blk_sq_make_request(struct request_queue *q, struct bio *bio)
 		}
 		list_add_tail(&rq->queuelist, &plug->mq_list);
 		blk_mq_put_ctx(data.ctx);
-		return BLK_QC_T_NONE;
+		return cookie;
 	}
 
 	if (!blk_mq_merge_queue_io(data.hctx, data.ctx, rq, bio)) {
@@ -1390,7 +1401,7 @@ run_queue:
 	}
 
 	blk_mq_put_ctx(data.ctx);
-	return BLK_QC_T_NONE;
+	return cookie;
 }
 
 /*
-- 
2.4.1.168.g1ea28e1

[PATCH 3/5] block: add block polling support

[Jens Axboe]

Add basic support for polling for specific IO to complete. This uses
the cookie that blk-mq passes back, which enables the block layer
to pass this cookie to the driver to spin for a specific request.

This will be combined with request latency tracking, so we can make
qualified decisions about when to poll and when not to. For now, for
benchmark purposes, we add a sysfs file that controls whether polling
is enabled or not.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/blk-core.c       | 41 +++++++++++++++++++++++++++++++++++++++++
 block/blk-mq-sysfs.c   | 10 ++++++++++
 block/blk-sysfs.c      | 35 +++++++++++++++++++++++++++++++++++
 include/linux/blk-mq.h | 10 ++++++++++
 include/linux/blkdev.h |  3 +++
 5 files changed, 99 insertions(+)

diff --git a/block/blk-core.c b/block/blk-core.c
index e93df6d386a0..fa36b4ff7d63 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -3312,6 +3312,47 @@ void blk_finish_plug(struct blk_plug *plug)
 }
 EXPORT_SYMBOL(blk_finish_plug);
 
+bool blk_poll(struct request_queue *q, blk_qc_t cookie)
+{
+	struct blk_plug *plug;
+	long state;
+
+	if (!q->mq_ops || !q->mq_ops->poll || !blk_qc_t_valid(cookie) ||
+	    !test_bit(QUEUE_FLAG_POLL, &q->queue_flags))
+		return false;
+
+	plug = current->plug;
+	if (plug)
+		blk_flush_plug_list(plug, false);
+
+	state = current->state;
+	while (!need_resched()) {
+		unsigned int queue_num = blk_qc_t_to_queue_num(cookie);
+		struct blk_mq_hw_ctx *hctx = q->queue_hw_ctx[queue_num];
+		int ret;
+
+		hctx->poll_invoked++;
+
+		ret = q->mq_ops->poll(hctx, blk_qc_t_to_tag(cookie));
+		if (ret > 0) {
+			hctx->poll_success++;
+			set_current_state(TASK_RUNNING);
+			return true;
+		}
+
+		if (signal_pending_state(state, current))
+			set_current_state(TASK_RUNNING);
+
+		if (current->state == TASK_RUNNING)
+			return true;
+		if (ret < 0)
+			break;
+		cpu_relax();
+	}
+
+	return false;
+}
+
 #ifdef CONFIG_PM
 /**
  * blk_pm_runtime_init - Block layer runtime PM initialization routine
diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 6f57a110289c..1cf18784c5cf 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -174,6 +174,11 @@ static ssize_t blk_mq_sysfs_rq_list_show(struct blk_mq_ctx *ctx, char *page)
 	return ret;
 }
 
+static ssize_t blk_mq_hw_sysfs_poll_show(struct blk_mq_hw_ctx *hctx, char *page)
+{
+	return sprintf(page, "invoked=%lu, success=%lu\n", hctx->poll_invoked, hctx->poll_success);
+}
+
 static ssize_t blk_mq_hw_sysfs_queued_show(struct blk_mq_hw_ctx *hctx,
 					   char *page)
 {
@@ -295,6 +300,10 @@ static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_cpus = {
 	.attr = {.name = "cpu_list", .mode = S_IRUGO },
 	.show = blk_mq_hw_sysfs_cpus_show,
 };
+static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_poll = {
+	.attr = {.name = "io_poll", .mode = S_IRUGO },
+	.show = blk_mq_hw_sysfs_poll_show,
+};
 
 static struct attribute *default_hw_ctx_attrs[] = {
 	&blk_mq_hw_sysfs_queued.attr,
@@ -304,6 +313,7 @@ static struct attribute *default_hw_ctx_attrs[] = {
 	&blk_mq_hw_sysfs_tags.attr,
 	&blk_mq_hw_sysfs_cpus.attr,
 	&blk_mq_hw_sysfs_active.attr,
+	&blk_mq_hw_sysfs_poll.attr,
 	NULL,
 };
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 31849e328b45..565b8dac5782 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -317,6 +317,34 @@ queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count)
 	return ret;
 }
 
+static ssize_t queue_poll_show(struct request_queue *q, char *page)
+{
+	return queue_var_show(test_bit(QUEUE_FLAG_POLL, &q->queue_flags), page);
+}
+
+static ssize_t queue_poll_store(struct request_queue *q, const char *page,
+				size_t count)
+{
+	unsigned long poll_on;
+	ssize_t ret;
+
+	if (!q->mq_ops || !q->mq_ops->poll)
+		return -EINVAL;
+
+	ret = queue_var_store(&poll_on, page, count);
+	if (ret < 0)
+		return ret;
+
+	spin_lock_irq(q->queue_lock);
+	if (poll_on)
+		queue_flag_set(QUEUE_FLAG_POLL, q);
+	else
+		queue_flag_clear(QUEUE_FLAG_POLL, q);
+	spin_unlock_irq(q->queue_lock);
+
+	return ret;
+}
+
 static struct queue_sysfs_entry queue_requests_entry = {
 	.attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
 	.show = queue_requests_show,
@@ -442,6 +470,12 @@ static struct queue_sysfs_entry queue_random_entry = {
 	.store = queue_store_random,
 };
 
+static struct queue_sysfs_entry queue_poll_entry = {
+	.attr = {.name = "io_poll", .mode = S_IRUGO | S_IWUSR },
+	.show = queue_poll_show,
+	.store = queue_poll_store,
+};
+
 static struct attribute *default_attrs[] = {
 	&queue_requests_entry.attr,
 	&queue_ra_entry.attr,
@@ -466,6 +500,7 @@ static struct attribute *default_attrs[] = {
 	&queue_rq_affinity_entry.attr,
 	&queue_iostats_entry.attr,
 	&queue_random_entry.attr,
+	&queue_poll_entry.attr,
 	NULL,
 };
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 83cc9d4e5455..daf17d70aeca 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -59,6 +59,9 @@ struct blk_mq_hw_ctx {
 
 	struct blk_mq_cpu_notifier	cpu_notifier;
 	struct kobject		kobj;
+
+	unsigned long		poll_invoked;
+	unsigned long		poll_success;
 };
 
 struct blk_mq_tag_set {
@@ -97,6 +100,8 @@ typedef void (exit_request_fn)(void *, struct request *, unsigned int,
 typedef void (busy_iter_fn)(struct blk_mq_hw_ctx *, struct request *, void *,
 		bool);
 typedef void (busy_tag_iter_fn)(struct request *, void *, bool);
+typedef int (poll_fn)(struct blk_mq_hw_ctx *, unsigned int);
+
 
 struct blk_mq_ops {
 	/*
@@ -114,6 +119,11 @@ struct blk_mq_ops {
 	 */
 	timeout_fn		*timeout;
 
+	/*
+	 * Called to poll for completion of a specific tag.
+	 */
+	poll_fn			*poll;
+
 	softirq_done_fn		*complete;
 
 	/*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 5ee0f5243025..3fe27f8d91f0 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -487,6 +487,7 @@ struct request_queue {
 #define QUEUE_FLAG_DEAD        19	/* queue tear-down finished */
 #define QUEUE_FLAG_INIT_DONE   20	/* queue is initialized */
 #define QUEUE_FLAG_NO_SG_MERGE 21	/* don't attempt to merge SG segments*/
+#define QUEUE_FLAG_POLL	       22	/* IO polling enabled if set */
 
 #define QUEUE_FLAG_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
 				 (1 << QUEUE_FLAG_STACKABLE)	|	\
@@ -814,6 +815,8 @@ extern int blk_execute_rq(struct request_queue *, struct gendisk *,
 extern void blk_execute_rq_nowait(struct request_queue *, struct gendisk *,
 				  struct request *, int, rq_end_io_fn *);
 
+bool blk_poll(struct request_queue *q, blk_qc_t cookie);
+
 static inline struct request_queue *bdev_get_queue(struct block_device *bdev)
 {
 	return bdev->bd_disk->queue;	/* this is never NULL */
-- 
2.4.1.168.g1ea28e1

[PATCH 4/5] NVMe: add blk polling support

[Jens Axboe]

Add nvme_poll(), which will check a specific completion queue for
command completions. Wire that up to the new block layer poll
mechanism.

Later on we'll setup specific sq/cq pairs that don't have interrups
enabled, so we can do more efficient polling. As of this patch, an
IRQ will still trigger on command completion.

Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/nvme/host/pci.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index e878590e71b6..4a715f49f5db 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -90,7 +90,7 @@ static struct class *nvme_class;
 
 static int __nvme_reset(struct nvme_dev *dev);
 static int nvme_reset(struct nvme_dev *dev);
-static int nvme_process_cq(struct nvme_queue *nvmeq);
+static void nvme_process_cq(struct nvme_queue *nvmeq);
 static void nvme_dead_ctrl(struct nvme_dev *dev);
 
 struct async_cmd_info {
@@ -935,7 +935,7 @@ static int nvme_queue_rq(struct blk_mq_hw_ctx *hctx,
 	return BLK_MQ_RQ_QUEUE_BUSY;
 }
 
-static int nvme_process_cq(struct nvme_queue *nvmeq)
+static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int *tag)
 {
 	u16 head, phase;
 
@@ -953,6 +953,8 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
 			head = 0;
 			phase = !phase;
 		}
+		if (tag && *tag == cqe.command_id)
+			*tag = -1;
 		ctx = nvme_finish_cmd(nvmeq, cqe.command_id, &fn);
 		fn(nvmeq, ctx, &cqe);
 	}
@@ -964,14 +966,18 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
 	 * a big problem.
 	 */
 	if (head == nvmeq->cq_head && phase == nvmeq->cq_phase)
-		return 0;
+		return;
 
 	writel(head, nvmeq->q_db + nvmeq->dev->db_stride);
 	nvmeq->cq_head = head;
 	nvmeq->cq_phase = phase;
 
 	nvmeq->cqe_seen = 1;
-	return 1;
+}
+
+static void nvme_process_cq(struct nvme_queue *nvmeq)
+{
+	__nvme_process_cq(nvmeq, NULL);
 }
 
 static irqreturn_t nvme_irq(int irq, void *data)
@@ -995,6 +1001,23 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
 	return IRQ_WAKE_THREAD;
 }
 
+static int nvme_poll(struct blk_mq_hw_ctx *hctx, unsigned int tag)
+{
+	struct nvme_queue *nvmeq = hctx->driver_data;
+
+	if ((le16_to_cpu(nvmeq->cqes[nvmeq->cq_head].status) & 1) ==
+	    nvmeq->cq_phase) {
+		spin_lock_irq(&nvmeq->q_lock);
+		__nvme_process_cq(nvmeq, &tag);
+		spin_unlock_irq(&nvmeq->q_lock);
+
+		if (tag == -1)
+			return 1;
+	}
+
+	return 0;
+}
+
 /*
  * Returns 0 on success.  If the result is negative, it's a Linux error code;
  * if the result is positive, it's an NVM Express status code
@@ -1654,6 +1677,7 @@ static struct blk_mq_ops nvme_mq_ops = {
 	.init_hctx	= nvme_init_hctx,
 	.init_request	= nvme_init_request,
 	.timeout	= nvme_timeout,
+	.poll		= nvme_poll,
 };
 
 static void nvme_dev_remove_admin(struct nvme_dev *dev)
-- 
2.4.1.168.g1ea28e1

RE: [PATCH 4/5] NVMe: add blk polling support

[Elliott, Robert (Persistent Memory)]

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Jens Axboe
> Sent: Friday, November 6, 2015 11:20 AM
...
> Subject: [PATCH 4/5] NVMe: add blk polling support
> 
> Add nvme_poll(), which will check a specific completion queue for
> command completions. Wire that up to the new block layer poll
> mechanism.
> 
> Later on we'll setup specific sq/cq pairs that don't have interrups
> enabled, so we can do more efficient polling. As of this patch, an
> IRQ will still trigger on command completion.
...
> -static int nvme_process_cq(struct nvme_queue *nvmeq)
> +static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int
> *tag)
>  {
>  	u16 head, phase;
> 
> @@ -953,6 +953,8 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
>  			head = 0;
>  			phase = !phase;
>  		}
> +		if (tag && *tag == cqe.command_id)
> +			*tag = -1;
>  		ctx = nvme_finish_cmd(nvmeq, cqe.command_id, &fn);
>  		fn(nvmeq, ctx, &cqe);
>  	}

The NVMe completion queue entries are 16 bytes long.  Although it's 
most likely to write them from 0..15 in one PCIe Memory Write
transaction, the NVMe device could write those bytes in any order.
It could thus update the command identifier before the other bytes,
causing this code to process invalid stale values in the other
fields.

When using interrupts, the MSI-X interrupt ensures the whole entry
is updated first, since it is delivered with a PCIe Memory Write
transaction and upstream writes do not pass upstream writes.

The existing interrupt handler loops looking for additional
completions, so is susceptible to this same problem - it's 
just less likely.  The only concern is completions that are 
added while the CPU is in the interrupt handler.

---
Robert Elliott, HPE Persistent Memory

Re: [PATCH 4/5] NVMe: add blk polling support

[Keith Busch]

On Fri, Nov 06, 2015 at 03:46:07PM -0800, Elliott, Robert (Persistent Memory) wrote:
> > -----Original Message-----
> > From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> > owner@vger.kernel.org] On Behalf Of Jens Axboe
> > Sent: Friday, November 6, 2015 11:20 AM
> ...
> > Subject: [PATCH 4/5] NVMe: add blk polling support
> >
> > Add nvme_poll(), which will check a specific completion queue for
> > command completions. Wire that up to the new block layer poll
> > mechanism.
> >
> > Later on we'll setup specific sq/cq pairs that don't have interrups
> > enabled, so we can do more efficient polling. As of this patch, an
> > IRQ will still trigger on command completion.
> ...
> > -static int nvme_process_cq(struct nvme_queue *nvmeq)
> > +static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int
> > *tag)
> >  {
> >       u16 head, phase;
> >
> > @@ -953,6 +953,8 @@ static int nvme_process_cq(struct nvme_queue *nvmeq)
> >                       head = 0;
> >                       phase = !phase;
> >               }
> > +             if (tag && *tag == cqe.command_id)
> > +                     *tag = -1;
> >               ctx = nvme_finish_cmd(nvmeq, cqe.command_id, &fn);
> >               fn(nvmeq, ctx, &cqe);
> >       }
> 
> The NVMe completion queue entries are 16 bytes long.  Although it's
> most likely to write them from 0..15 in one PCIe Memory Write
> transaction, the NVMe device could write those bytes in any order.
> It could thus update the command identifier before the other bytes,
> causing this code to process invalid stale values in the other
> fields.

That's a very interesting point. We are okay if we can rely on the phase
bit, which we can by my reading of the spec. Coalescing would not work
if the driver can observe a new phase in a partially written CQE.

RE: [PATCH 4/5] NVMe: add blk polling support

[Elliott, Robert (Persistent Memory)]

> -----Original Message-----
> From: Keith Busch [mailto:keith.busch@intel.com]
> Sent: Friday, November 6, 2015 6:58 PM
> Subject: Re: [PATCH 4/5] NVMe: add blk polling support
> 
> On Fri, Nov 06, 2015 at 03:46:07PM -0800, Elliott, Robert wrote:
> > > -----Original Message-----
> > > From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> > > owner@vger.kernel.org] On Behalf Of Jens Axboe
> > > Sent: Friday, November 6, 2015 11:20 AM
> > ...
> > > Subject: [PATCH 4/5] NVMe: add blk polling support
> > >
> > > @@ -953,6 +953,8 @@ static int nvme_process_cq(struct nvme_queue
> *nvmeq)
> > >                       head = 0;
> > >                       phase = !phase;
> > >               }
> > > +             if (tag && *tag == cqe.command_id)
> > > +                     *tag = -1;
> > >               ctx = nvme_finish_cmd(nvmeq, cqe.command_id, &fn);
> > >               fn(nvmeq, ctx, &cqe);
> > >       }
> >
> > The NVMe completion queue entries are 16 bytes long.  Although it's
> > most likely to write them from 0..15 in one PCIe Memory Write
> > transaction, the NVMe device could write those bytes in any order.
> > It could thus update the command identifier before the other bytes,
> > causing this code to process invalid stale values in the other
> > fields.
> 
> That's a very interesting point. We are okay if we can rely on the phase
> bit, which we can by my reading of the spec. Coalescing would not work
> if the driver can observe a new phase in a partially written CQE.

The Phase bit is in the same Dword as the Command Identifier, so
it doesn't help.  If that Dword were written first, then the
preceding three Dwords might not be valid yet.

I'll ask our NVMe representative to propose wording like this:

  4.6 Completion Queue Entry
  ...
  The controller shall write the Dwords in a CQE from lowest to highest 
  (e.g., if the CQE is 16 bytes, write Dword 0, then Dword 1, then
  Dword 2, then Dword 3).  This ensures that the first three Dwords are
  valid when the Phase Tag and Command Identifier are valid. Additional
  Dwords, if any, are not valid at that time.

and refer to that rule in 7.1 where host processing of completions
is discussed.

---
Robert Elliott, HPE Persistent Memory

[PATCH 5/5] directio: add block polling support

[Jens Axboe]

This adds support for sync O_DIRECT read/write poll support.

Signed-off-by: Jens Axboe <axboe@fb.com>
[hch: split from a larger patch, minor updates]
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/direct-io.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 3ae0e0427191..7025029c666f 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -109,6 +109,8 @@ struct dio_submit {
 struct dio {
 	int flags;			/* doesn't change */
 	int rw;
+	blk_qc_t bio_cookie;
+	struct block_device *bio_bdev;
 	struct inode *inode;
 	loff_t i_size;			/* i_size when submitted */
 	dio_iodone_t *end_io;		/* IO completion function */
@@ -397,11 +399,14 @@ static inline void dio_bio_submit(struct dio *dio, struct dio_submit *sdio)
 	if (dio->is_async && dio->rw == READ && dio->should_dirty)
 		bio_set_pages_dirty(bio);
 
-	if (sdio->submit_io)
+	if (sdio->submit_io) {
 		sdio->submit_io(dio->rw, bio, dio->inode,
 			       sdio->logical_offset_in_bio);
-	else
-		submit_bio(dio->rw, bio);
+		dio->bio_cookie = BLK_QC_T_NONE;
+	} else {
+		dio->bio_cookie = submit_bio(dio->rw, bio);
+		dio->bio_bdev = bio->bi_bdev;
+	}
 
 	sdio->bio = NULL;
 	sdio->boundary = 0;
@@ -440,7 +445,8 @@ static struct bio *dio_await_one(struct dio *dio)
 		__set_current_state(TASK_UNINTERRUPTIBLE);
 		dio->waiter = current;
 		spin_unlock_irqrestore(&dio->bio_lock, flags);
-		io_schedule();
+		if (!blk_poll(bdev_get_queue(dio->bio_bdev), dio->bio_cookie))
+			io_schedule();
 		/* wake up sets us TASK_RUNNING */
 		spin_lock_irqsave(&dio->bio_lock, flags);
 		dio->waiter = NULL;
-- 
2.4.1.168.g1ea28e1

Re: [PATCH 0/5] Initial support for polled IO

[Keith Busch]

On Fri, Nov 06, 2015 at 10:20:18AM -0700, Jens Axboe wrote:
> Hi,
> 
> This is a basic framework for supporting polled IO with the block
> layer stack, and added support for sync O_DIRECT IO and the NVMe
> driver.
> 
> There are a few things missing to truly productize this, but it's
> very useful for testing. For now, it's a per-device opt-in feature.
> To enable it, you echo 1 to /sys/block/<dev>/queue/io_poll.

This really looks good. I verified similar performance improvements on
various NVMe controller types as well.

Acked-by: Keith Busch <keith.busch@intel.com>

Re: [PATCH 0/5] Initial support for polled IO

[Christoph Hellwig]

Hi Jens,

this looks great.  We're seeing some similarly good results.  I don't
think this is actually usable for applications as-is, but it's a) very
useful for benchmarking, and b) allows us to develop the proper
interfaces on top.  So let's ship it!

Acked-by: Christoph Hellwig <hch@lst.de>