Re: [PATCH v4 01/10] xen/blkif: document blkif multi-queue/ring extension

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Mon, Nov 02, 2015 at 12:21:37PM +0800, Bob Liu wrote:
> 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>

I queued this up, but obviously we need to wait for the Xen version to
be accepted.

> --
> v2:
> Add descriptions together with multi-page ring buffer.
> ---
>  include/xen/interface/io/blkif.h | 48 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 48 insertions(+)
> 
> diff --git a/include/xen/interface/io/blkif.h b/include/xen/interface/io/blkif.h
> index c33e1c4..8b8cfad 100644
> --- a/include/xen/interface/io/blkif.h
> +++ b/include/xen/interface/io/blkif.h
> @@ -28,6 +28,54 @@ 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.
>   */
>  #define BLKIF_OP_READ              0
> -- 
> 1.8.3.1
>