From eb5df87fab0ae7114b83dc7f338b27d039374767 Mon Sep 17 00:00:00 2001 From: Bob Liu Date: Sat, 14 Nov 2015 11:12:10 +0800 Subject: 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: Bob Liu Signed-off-by: Konrad Rzeszutek Wilk --- include/xen/interface/io/blkif.h | 48 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) (limited to 'include') diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h index c33e1c489eb2..8b8cfadf7833 100644 --- a/include/xen/interface/io/blkif.h +++ b/include/xen/interface/io/blkif.h @@ -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 = "" + * /local/domain/1/device/vbd/0/queue-0/event-channel = "" + * /local/domain/1/device/vbd/0/queue-1 = "" + * /local/domain/1/device/vbd/0/queue-1/ring-ref = "" + * /local/domain/1/device/vbd/0/queue-1/event-channel = "" + * + * 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 = "" + * /local/domain/1/device/vbd/0/queue-0/ring-ref1 = "" + * /local/domain/1/device/vbd/0/queue-0/event-channel = "" + * /local/domain/1/device/vbd/0/queue-1 = "" + * /local/domain/1/device/vbd/0/queue-1/ring-ref0 = "" + * /local/domain/1/device/vbd/0/queue-1/ring-ref1 = "" + * /local/domain/1/device/vbd/0/queue-1/event-channel = "" + * + */ + /* * REQUEST CODES. */ -- cgit v1.2.3