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Re: [Xen-devel] [PATCH V4 net-next 5/5] xen-net{back, front}: Document multi-queue feature in netif.h

On 21/02/14 12:22, Paul Durrant wrote:
-----Original Message-----
From: Andrew J. Bennieston [mailto:andrew.bennieston@xxxxxxxxxx]
Sent: 17 February 2014 17:58
To: xen-devel@xxxxxxxxxxxxxxxxxxxx
Cc: Ian Campbell; Wei Liu; Paul Durrant; netdev@xxxxxxxxxxxxxxx; David
Vrabel; Andrew Bennieston
Subject: [PATCH V4 net-next 5/5] xen-net{back,front}: Document multi-
queue feature in netif.h

From: "Andrew J. Bennieston" <andrew.bennieston@xxxxxxxxxx>

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

Signed-off-by: Andrew J. Bennieston <andrew.bennieston@xxxxxxxxxx>
  include/xen/interface/io/netif.h |   21 +++++++++++++++++++++
  1 file changed, 21 insertions(+)

diff --git a/include/xen/interface/io/netif.h
index c50061d..8868c51 100644
--- a/include/xen/interface/io/netif.h
+++ b/include/xen/interface/io/netif.h
@@ -51,6 +51,27 @@

+ * Multiple transmit and receive queues:
+ * If supported, the backend will write "multi-queue-max-queues" and set
+ * 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", set to the number they wish to use.
+ *
+ * Queues replicate the shared rings and event channels, and
+ * "feature-split-event-channels" is required when using multiple queues.
+ *

Is it? The code in patch 2 appears to cope with the "event-channel" key as well 
as the split variants regardless of the number of queues being used. Am I missing some 
other restriction?

Hmm, perhaps I just assumed that limitation. I'll check and update the doc accordingly.



+ * 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 them under sub-keys
+ * the name "queue-N" where N is the integer ID of the queue for which
+ * keys belong. Queues are indexed from zero.
+ */
   * "feature-no-csum-offload" should be used to turn IPv4 TCP/UDP
   * offload off or on. If it is missing then the feature is assumed to be on.
   * "feature-ipv6-csum-offload" should be used to turn IPv6 TCP/UDP

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