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

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

Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Bob Liu 2015-11-14 11:12:10 +08:00 committed by Konrad Rzeszutek Wilk
parent 627ccd20b4
commit eb5df87fab
1 changed files with 48 additions and 0 deletions
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48
include/xen/interface/io/blkif.h
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@ -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.
*/