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Commit eb5df87f authored by Bob Liu's avatar Bob Liu Committed by Konrad Rzeszutek Wilk
Browse files

xen/blkif: document blkif multi-queue/ring extension 



Document the multi-queue/ring feature in terms of XenStore keys to be written by
the backend and by the frontend.

Signed-off-by: default avatarBob Liu <bob.liu@oracle.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent 627ccd20

include/xen/interface/io/blkif.h

+48 −0
Original line number Diff line number Diff line
@@ -27,6 +27,54 @@ 
typedef uint16_t blkif_vdev_t;

typedef uint64_t blkif_sector_t;



/*

 * Multiple hardware queues/rings:

 * If supported, the backend will write the key "multi-queue-max-queues" to

 * the directory for that vbd, and set its value to the maximum supported

 * number of queues.

 * Frontends that are aware of this feature and wish to use it can write the

 * key "multi-queue-num-queues" with the number they wish to use, which must be

 * greater than zero, and no more than the value reported by the backend in

 * "multi-queue-max-queues".

 *

 * For frontends requesting just one queue, the usual event-channel and

 * ring-ref keys are written as before, simplifying the backend processing

 * to avoid distinguishing between a frontend that doesn't understand the

 * multi-queue feature, and one that does, but requested only one queue.

 *

 * Frontends requesting two or more queues must not write the toplevel

 * event-channel and ring-ref keys, instead writing those keys under sub-keys

 * having the name "queue-N" where N is the integer ID of the queue/ring for

 * which those keys belong. Queues are indexed from zero.

 * For example, a frontend with two queues must write the following set of

 * queue-related keys:

 *

 * /local/domain/1/device/vbd/0/multi-queue-num-queues = "2"

 * /local/domain/1/device/vbd/0/queue-0 = ""

 * /local/domain/1/device/vbd/0/queue-0/ring-ref = "<ring-ref#0>"

 * /local/domain/1/device/vbd/0/queue-0/event-channel = "<evtchn#0>"

 * /local/domain/1/device/vbd/0/queue-1 = ""

 * /local/domain/1/device/vbd/0/queue-1/ring-ref = "<ring-ref#1>"

 * /local/domain/1/device/vbd/0/queue-1/event-channel = "<evtchn#1>"

 *

 * It is also possible to use multiple queues/rings together with

 * feature multi-page ring buffer.

 * For example, a frontend requests two queues/rings and the size of each ring

 * buffer is two pages must write the following set of related keys:

 *

 * /local/domain/1/device/vbd/0/multi-queue-num-queues = "2"

 * /local/domain/1/device/vbd/0/ring-page-order = "1"

 * /local/domain/1/device/vbd/0/queue-0 = ""

 * /local/domain/1/device/vbd/0/queue-0/ring-ref0 = "<ring-ref#0>"

 * /local/domain/1/device/vbd/0/queue-0/ring-ref1 = "<ring-ref#1>"

 * /local/domain/1/device/vbd/0/queue-0/event-channel = "<evtchn#0>"

 * /local/domain/1/device/vbd/0/queue-1 = ""

 * /local/domain/1/device/vbd/0/queue-1/ring-ref0 = "<ring-ref#2>"

 * /local/domain/1/device/vbd/0/queue-1/ring-ref1 = "<ring-ref#3>"

 * /local/domain/1/device/vbd/0/queue-1/event-channel = "<evtchn#1>"

 *

 */



/*

 * REQUEST CODES.

 */