Documentation/ABI/rnbd-clt: Add description for nr_poll_queues

describe how to set nr_poll_queues and enable the polling
Signed-off-by: Gioh Kim <gi-oh.kim@ionos.com>
Acked-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Link: https://lore.kernel.org/r/20210419073722.15351-15-gi-oh.kim@ionos.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Documentation/ABI/testing/sysfs-block-rnbd

@@ -56,3 +56,9 @@ Date:		Feb 2020
 KernelVersion:	5.7
 Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
 Description:	Remap the disconnected device if the session is not destroyed yet.
+
+What:		/sys/block/rnbd<N>/rnbd/nr_poll_queues
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Contains the number of poll-mode queues

Documentation/ABI/testing/sysfs-class-rnbd-client

@@ -85,6 +85,19 @@ Description:	Expected format is the following::
 
 		By default "rw" is used.
 
+		nr_poll_queues
+		  specifies the number of poll-mode queues. If the IO has HIPRI flag,
+		  the block-layer will send the IO via the poll-mode queue.
+		  For fast network and device the polling is faster than interrupt-base
+		  IO handling because it saves time for context switching, switching to
+		  another process, handling the interrupt and switching back to the
+		  issuing process.
+
+		  Set -1 if you want to set it as the number of CPUs
+		  By default rnbd client creates only irq-mode queues.
+
+		  NOTICE: MUST make a unique session for a device using the poll-mode queues.
+
 		Exit Codes:
 
 		If the device is already mapped it will fail with EEXIST. If the input