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xen-net{back, front}: Document multi-queue feature in netif.h 

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@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Andrew J. Bennieston 2014-06-04 10:30:46 +01:00 committed by David S. Miller
parent 50ee60611b
commit a2deb8b1e7
1 changed files with 53 additions and 0 deletions
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53
include/xen/interface/io/netif.h
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@ -50,6 +50,59 @@
* node as before.
*/
/*
* Multiple transmit and receive queues:
* If supported, the backend will write the key "multi-queue-max-queues" to
* the directory for that vif, 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", set to 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".
*
* Queues replicate the shared rings and event channels.
* "feature-split-event-channels" may optionally be used when using
* multiple queues, but is not mandatory.
*
* Each queue consists of one shared ring pair, i.e. there must be the same
* number of tx and rx rings.
*
* 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 (or event-channel-{tx,rx}) and {tx,rx}-ring-ref keys,
* instead writing those keys under sub-keys having the name "queue-N" where
* N is the integer ID of the queue for which those keys belong. Queues
* are indexed from zero. For example, a frontend with two queues and split
* event channels must write the following set of queue-related keys:
*
* /local/domain/1/device/vif/0/multi-queue-num-queues = "2"
* /local/domain/1/device/vif/0/queue-0 = ""
* /local/domain/1/device/vif/0/queue-0/tx-ring-ref = "<ring-ref-tx0>"
* /local/domain/1/device/vif/0/queue-0/rx-ring-ref = "<ring-ref-rx0>"
* /local/domain/1/device/vif/0/queue-0/event-channel-tx = "<evtchn-tx0>"
* /local/domain/1/device/vif/0/queue-0/event-channel-rx = "<evtchn-rx0>"
* /local/domain/1/device/vif/0/queue-1 = ""
* /local/domain/1/device/vif/0/queue-1/tx-ring-ref = "<ring-ref-tx1>"
* /local/domain/1/device/vif/0/queue-1/rx-ring-ref = "<ring-ref-rx1"
* /local/domain/1/device/vif/0/queue-1/event-channel-tx = "<evtchn-tx1>"
* /local/domain/1/device/vif/0/queue-1/event-channel-rx = "<evtchn-rx1>"
*
* If there is any inconsistency in the XenStore data, the backend may
* choose not to connect any queues, instead treating the request as an
* error. This includes scenarios where more (or fewer) queues were
* requested than the frontend provided details for.
*
* Mapping of packets to queues is considered to be a function of the
* transmitting system (backend or frontend) and is not negotiated
* between the two. Guests are free to transmit packets on any queue
* they choose, provided it has been set up correctly. Guests must be
* prepared to receive packets on any queue they have requested be set up.
*/
/*
* "feature-no-csum-offload" should be used to turn IPv4 TCP/UDP checksum
* offload off or on. If it is missing then the feature is assumed to be on.