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[PATCH v4 01/10] 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>
--
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

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Thread

[PATCH v4 00/10] xen-block: multi hardware-queues/rings support Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
  [PATCH v4 05/10] xen/blkfront: negotiate number of queues/rings to be used with backend Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
    Re: [PATCH v4 05/10] xen/blkfront: negotiate number of queues/rings  to be used with backend Bob Liu <bob.liu@oracle.com> - 2015-11-04 02:20 +0100
      Re: [PATCH v4 05/10] xen/blkfront: negotiate number of queues/rings  to be used with backend Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2015-11-04 03:00 +0100
  [PATCH v4 04/10] xen/blkfront: split per device io_lock Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
    Re: [PATCH v4 04/10] xen/blkfront: split per device io_lock Bob Liu <bob.liu@oracle.com> - 2015-11-04 02:10 +0100
      Re: [PATCH v4 04/10] xen/blkfront: split per device io_lock Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2015-11-04 03:00 +0100
  [PATCH v4 07/10] xen/blkback: pseudo support for multi hardware queues/rings Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
    Re: [PATCH v4 07/10] xen/blkback: pseudo support for multi hardware  queues/rings Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2015-11-05 03:40 +0100
      Re: [PATCH v4 07/10] xen/blkback: pseudo support for multi hardware  queues/rings Bob Liu <bob.liu@oracle.com> - 2015-11-05 04:10 +0100
        Re: [PATCH v4 07/10] xen/blkback: pseudo support for multi hardware queues/rings Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2015-11-05 04:30 +0100
  [PATCH v4 09/10] xen/blkfront: make persistent grants per-queue Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
    Re: [PATCH v4 09/10] xen/blkfront: make persistent grants per-queue Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2015-11-05 03:40 +0100
  [PATCH v4 06/10] xen/blkback: separate ring information out of struct xen_blkif Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
  [PATCH v4 02/10] xen/blkfront: separate per ring information out of device info Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
  [PATCH v4 08/10] xen/blkback: get the number of hardware queues/rings from blkfront Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
    Re: [PATCH v4 08/10] xen/blkback: get the number of hardware  queues/rings from blkfront Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> - 2015-11-05 03:40 +0100
  [PATCH v4 01/10] xen/blkif: document blkif multi-queue/ring extension Bob Liu <bob.liu@oracle.com> - 2015-11-02 05:30 +0100
  Re: [Xen-devel] [PATCH v4 00/10] xen-block: multi hardware-queues/rings  support Julien Grall <julien.grall@citrix.com> - 2015-11-02 12:30 +0100

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