zvol: Support blk-mq for better performance

Add support for the kernel's block multiqueue (blk-mq) interface in
the zvol block driver.  blk-mq creates multiple request queues on
different CPUs rather than having a single request queue.  This can
improve zvol performance with multithreaded reads/writes.

This implementation uses the blk-mq interfaces on 4.13 or newer
kernels.  Building against older kernels will fall back to the
older BIO interfaces.

Note that you must set the `zvol_use_blk_mq` module param to
enable the blk-mq API.  It is disabled by default.

In addition, this commit lets the zvol blk-mq layer process whole
`struct request` IOs at a time, rather than breaking them down
into their individual BIOs.  This reduces dbuf lock contention
and overhead versus the legacy zvol submit_bio() codepath.

	sequential dd to one zvol, 8k volblocksize, no O_DIRECT:

	legacy submit_bio()     292MB/s write  453MB/s read
	this commit             453MB/s write  885MB/s read

It also introduces a new `zvol_blk_mq_chunks_per_thread` module
parameter. This parameter represents how many volblocksize'd chunks
to process per each zvol thread.  It can be used to tune your zvols
for better read vs write performance (higher values favor write,
lower favor read).

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Ahelenia Ziemiańska <[email protected]>
Reviewed-by: Tony Nguyen <[email protected]>
Signed-off-by: Tony Hutter <[email protected]>
Closes #13148
Issue #12483

config/kernel-blk-queue.m4

@@ -359,6 +359,36 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_MAX_SEGMENTS], [
 	])
 ])
 
+dnl #
+dnl # See if kernel supports block multi-queue and blk_status_t.
+dnl # blk_status_t represents the new status codes introduced in the 4.13
+dnl # kernel patch:
+dnl #
+dnl #  block: introduce new block status code type
+dnl #
+dnl # We do not currently support the "old" block multi-queue interfaces from
+dnl # prior kernels.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_MQ], [
+	ZFS_LINUX_TEST_SRC([blk_mq], [
+		#include <linux/blk-mq.h>
+	], [
+		struct blk_mq_tag_set tag_set __attribute__ ((unused)) = {0};
+		(void) blk_mq_alloc_tag_set(&tag_set);
+		return BLK_STS_OK;
+	], [])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_BLK_MQ], [
+	AC_MSG_CHECKING([whether block multiqueue with blk_status_t is available])
+	ZFS_LINUX_TEST_RESULT([blk_mq], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_BLK_MQ, 1, [block multiqueue is available])
+	], [
+		AC_MSG_RESULT(no)
+	])
+])
+
 AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE], [
 	ZFS_AC_KERNEL_SRC_BLK_QUEUE_PLUG
 	ZFS_AC_KERNEL_SRC_BLK_QUEUE_BDI
@@ -370,6 +400,7 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE], [
 	ZFS_AC_KERNEL_SRC_BLK_QUEUE_FLUSH
 	ZFS_AC_KERNEL_SRC_BLK_QUEUE_MAX_HW_SECTORS
 	ZFS_AC_KERNEL_SRC_BLK_QUEUE_MAX_SEGMENTS
+	ZFS_AC_KERNEL_SRC_BLK_MQ
 ])
 
 AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE], [
@@ -383,4 +414,5 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE], [
 	ZFS_AC_KERNEL_BLK_QUEUE_FLUSH
 	ZFS_AC_KERNEL_BLK_QUEUE_MAX_HW_SECTORS
 	ZFS_AC_KERNEL_BLK_QUEUE_MAX_SEGMENTS
+	ZFS_AC_KERNEL_BLK_MQ
 ])

include/os/linux/kernel/linux/blkdev_compat.h

@@ -34,6 +34,11 @@
 #include <linux/hdreg.h>
 #include <linux/major.h>
 #include <linux/msdos_fs.h>	/* for SECTOR_* */
+#include <linux/bio.h>
+
+#ifdef HAVE_BLK_MQ
+#include <linux/blk-mq.h>
+#endif
 
 #ifndef HAVE_BLK_QUEUE_FLAG_SET
 static inline void
@@ -608,4 +613,110 @@ blk_generic_alloc_queue(make_request_fn make_request, int node_id)
 }
 #endif /* !HAVE_SUBMIT_BIO_IN_BLOCK_DEVICE_OPERATIONS */
 
+/*
+ * All the io_*() helper functions below can operate on a bio, or a rq, but
+ * not both.  The older submit_bio() codepath will pass a bio, and the
+ * newer blk-mq codepath will pass a rq.
+ */
+static inline int
+io_data_dir(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL) {
+		if (op_is_write(req_op(rq))) {
+			return (WRITE);
+		} else {
+			return (READ);
+		}
+	}
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (bio_data_dir(bio));
+}
+
+static inline int
+io_is_flush(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (req_op(rq) == REQ_OP_FLUSH);
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (bio_is_flush(bio));
+}
+
+static inline int
+io_is_discard(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (req_op(rq) == REQ_OP_DISCARD);
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (bio_is_discard(bio));
+}
+
+static inline int
+io_is_secure_erase(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (req_op(rq) == REQ_OP_SECURE_ERASE);
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (bio_is_secure_erase(bio));
+}
+
+static inline int
+io_is_fua(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (rq->cmd_flags & REQ_FUA);
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (bio_is_fua(bio));
+}
+
+
+static inline uint64_t
+io_offset(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (blk_rq_pos(rq) << 9);
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (BIO_BI_SECTOR(bio) << 9);
+}
+
+static inline uint64_t
+io_size(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (blk_rq_bytes(rq));
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (BIO_BI_SIZE(bio));
+}
+
+static inline int
+io_has_data(struct bio *bio, struct request *rq)
+{
+#ifdef HAVE_BLK_MQ
+	if (rq != NULL)
+		return (bio_has_data(rq->bio));
+#else
+	ASSERT3P(rq, ==, NULL);
+#endif
+	return (bio_has_data(bio));
+}
 #endif /* _ZFS_BLKDEV_H */

include/os/linux/spl/sys/uio.h

@@ -69,9 +69,20 @@ typedef struct zfs_uio {
 	uint16_t	uio_fmode;
 	uint16_t	uio_extflg;
 	ssize_t		uio_resid;
+
 	size_t		uio_skip;
+
+	struct request	*rq;
+
+	/*
+	 * Used for saving rq_for_each_segment() state between calls
+	 * to zfs_uiomove_bvec_rq().
+	 */
+	struct req_iterator iter;
+	struct bio_vec bv;
 } zfs_uio_t;
 
+
 #define	zfs_uio_segflg(u)		(u)->uio_segflg
 #define	zfs_uio_offset(u)		(u)->uio_loffset
 #define	zfs_uio_resid(u)		(u)->uio_resid
@@ -116,17 +127,33 @@ zfs_uio_iovec_init(zfs_uio_t *uio, const struct iovec *iov,
 }
 
 static inline void
-zfs_uio_bvec_init(zfs_uio_t *uio, struct bio *bio)
+zfs_uio_bvec_init(zfs_uio_t *uio, struct bio *bio, struct request *rq)
 {
-	uio->uio_bvec = &bio->bi_io_vec[BIO_BI_IDX(bio)];
-	uio->uio_iovcnt = bio->bi_vcnt - BIO_BI_IDX(bio);
-	uio->uio_loffset = BIO_BI_SECTOR(bio) << 9;
+	/* Either bio or rq will be set, but not both */
+	ASSERT3P(uio, !=, bio);
+
+	if (bio) {
+		uio->uio_iovcnt = bio->bi_vcnt - BIO_BI_IDX(bio);
+		uio->uio_bvec = &bio->bi_io_vec[BIO_BI_IDX(bio)];
+	} else {
+		uio->uio_bvec = NULL;
+		uio->uio_iovcnt = 0;
+		memset(&uio->iter, 0, sizeof (uio->iter));
+	}
+
+	uio->uio_loffset = io_offset(bio, rq);
 	uio->uio_segflg = UIO_BVEC;
 	uio->uio_fault_disable = B_FALSE;
 	uio->uio_fmode = 0;
 	uio->uio_extflg = 0;
-	uio->uio_resid = BIO_BI_SIZE(bio);
-	uio->uio_skip = BIO_BI_SKIP(bio);
+	uio->uio_resid = io_size(bio, rq);
+	if (bio) {
+		uio->uio_skip = BIO_BI_SKIP(bio);
+	} else {
+		uio->uio_skip = 0;
+	}
+
+	uio->rq = rq;
 }
 
 #if defined(HAVE_VFS_IOV_ITER)

man/man4/zfs.4

@@ -2248,9 +2248,74 @@ for each I/O submitter.
 When unset, requests are handled asynchronously by a thread pool.
 The number of requests which can be handled concurrently is controlled by
 .Sy zvol_threads .
+.Sy zvol_request_sync
+is ignored when running on a kernel that supports block multiqueue
+.Pq Li blk-mq .
 .
-.It Sy zvol_threads Ns = Ns Sy 32 Pq uint
-Max number of threads which can handle zvol I/O requests concurrently.
+.It Sy zvol_threads Ns = Ns Sy 0 Pq uint
+The number of system wide threads to use for processing zvol block IOs.
+If
+.Sy 0
+(the default) then internally set
+.Sy zvol_threads
+to the number of CPUs present or 32 (whichever is greater).
+.
+.It Sy zvol_blk_mq_threads Ns = Ns Sy 0 Pq uint
+The number of threads per zvol to use for queuing IO requests.
+This parameter will only appear if your kernel supports
+.Li blk-mq
+and is only read and assigned to a zvol at zvol load time.
+If
+.Sy 0
+(the default) then internally set
+.Sy zvol_blk_mq_threads
+to the number of CPUs present.
+.
+.It Sy zvol_use_blk_mq Ns = Ns Sy 0 Ns | Ns 1 Pq uint
+Set to
+.Sy 1
+to use the
+.Li blk-mq
+API for zvols.
+Set to
+.Sy 0
+(the default) to use the legacy zvol APIs.
+This setting can give better or worse zvol performance depending on
+the workload.
+This parameter will only appear if your kernel supports
+.Li blk-mq
+and is only read and assigned to a zvol at zvol load time.
+.
+.It Sy zvol_blk_mq_blocks_per_thread Ns = Ns Sy 8 Pq uint
+If
+.Sy zvol_use_blk_mq
+is enabled, then process this number of
+.Sy volblocksize Ns -sized blocks per zvol thread.
+This tunable can be use to favor better performance for zvol reads (lower
+values) or writes (higher values).
+If set to
+.Sy 0 ,
+then the zvol layer will process the maximum number of blocks
+per thread that it can.
+This parameter will only appear if your kernel supports
+.Li blk-mq
+and is only applied at each zvol's load time.
+.
+.It Sy zvol_blk_mq_queue_depth Ns = Ns Sy 0 Pq uint
+The queue_depth value for the zvol
+.Li blk-mq
+interface.
+This parameter will only appear if your kernel supports
+.Li blk-mq
+and is only applied at each zvol's load time.
+If
+.Sy 0
+(the default) then use the kernel's default queue depth.
+Values are clamped to the kernel's
+.Dv BLKDEV_MIN_RQ
+and
+.Dv BLKDEV_MAX_RQ Ns / Ns Dv BLKDEV_DEFAULT_RQ
+limits.
 .
 .It Sy zvol_volmode Ns = Ns Sy 1 Pq uint
 Defines zvol block devices behaviour when