Revert "zvol: Temporally disable blk-mq"

This reverts commit aefb6a2bd6.

aefb6a2bd temporally disabled blk-mq until we could fix a fix for

Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #15439

man/man4/zfs.4

@@ -2317,6 +2317,63 @@ If
 .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
 .Sy volmode Ns = Ns Sy default :

module/os/linux/zfs/zvol_os.c

@@ -1620,6 +1620,18 @@ MODULE_PARM_DESC(zvol_prefetch_bytes, "Prefetch N bytes at zvol start+end");
 module_param(zvol_volmode, uint, 0644);
 MODULE_PARM_DESC(zvol_volmode, "Default volmode property value");
 
+#ifdef HAVE_BLK_MQ
+module_param(zvol_blk_mq_queue_depth, uint, 0644);
+MODULE_PARM_DESC(zvol_blk_mq_queue_depth, "Default blk-mq queue depth");
+
+module_param(zvol_use_blk_mq, uint, 0644);
+MODULE_PARM_DESC(zvol_use_blk_mq, "Use the blk-mq API for zvols");
+
+module_param(zvol_blk_mq_blocks_per_thread, uint, 0644);
+MODULE_PARM_DESC(zvol_blk_mq_blocks_per_thread,
+    "Process volblocksize blocks per thread");
+#endif
+
 #ifndef HAVE_BLKDEV_GET_ERESTARTSYS
 module_param(zvol_open_timeout_ms, uint, 0644);
 MODULE_PARM_DESC(zvol_open_timeout_ms, "Timeout for ZVOL open retries");

tests/zfs-tests/include/tunables.cfg

@@ -89,7 +89,7 @@ VDEV_VALIDATE_SKIP		vdev.validate_skip		vdev_validate_skip
 VOL_INHIBIT_DEV			UNSUPPORTED			zvol_inhibit_dev
 VOL_MODE			vol.mode			zvol_volmode
 VOL_RECURSIVE			vol.recursive			UNSUPPORTED
-VOL_USE_BLK_MQ			UNSUPPORTED			UNSUPPORTED
+VOL_USE_BLK_MQ			UNSUPPORTED			zvol_use_blk_mq
 XATTR_COMPAT			xattr_compat			zfs_xattr_compat
 ZEVENT_LEN_MAX			zevent.len_max			zfs_zevent_len_max
 ZEVENT_RETAIN_MAX		zevent.retain_max		zfs_zevent_retain_max