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

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Date:	Fri, 21 Feb 2014 12:24:01 +0000
From:	Andrew Bennieston <andrew.bennieston@...rix.com>
To:	Paul Durrant <Paul.Durrant@...rix.com>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
CC:	Ian Campbell <Ian.Campbell@...rix.com>,
	Wei Liu <wei.liu2@...rix.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [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@...rix.com]
>> Sent: 17 February 2014 17:58
>> To: xen-devel@...ts.xenproject.org
>> Cc: Ian Campbell; Wei Liu; Paul Durrant; netdev@...r.kernel.org; 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@...rix.com>
>>
>> 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@...rix.com>
>> ---
>>   include/xen/interface/io/netif.h |   21 +++++++++++++++++++++
>>   1 file changed, 21 insertions(+)
>>
>> diff --git a/include/xen/interface/io/netif.h
>> b/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
>> 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.
>> + *
>> + * 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.

Andrew

>    Paul
>
>> + * 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
>> having
>> + * the name "queue-N" where N is the integer ID of the queue for which
>> those
>> + * keys belong. Queues are indexed from zero.
>> + */
>> +
>> +/*
>>    * "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.
>>    * "feature-ipv6-csum-offload" should be used to turn IPv6 TCP/UDP
>> checksum
>> --
>> 1.7.10.4
>

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