Re: [Qemu-devel] [PATCH v10 6/7] vhost-user: add multiple queue support

[Eric Blake]

On 09/18/2015 08:58 AM, Yuanhan Liu wrote:
> From: Changchun Ouyang <address@hidden>
> 
> This patch is initially based a patch from Nikolay Nikolaev.
> 
> This patch adds vhost-user multiple queue support, by creating a nc
> and vhost_net pair for each queue.
> 
> Qemu exits if find that the backend can't support number of requested

s/support/support the/

> queues (by providing queues=# option). The max number is queried by a
> new message, VHOST_USER_GET_QUEUE_NUM, and is sent only when protocol
> feature VHOST_USER_PROTOCOL_F_MQ is present first.
> 
> The max queue check is done at vhost-user initiation stage. We initiate
> one queue first, which, in the meantime, also gets the max_queues the
> backend supports.
> 
> In older version, it was reported that some messages are sent more times
> than necessary. Here we came an agreement with Michael that we could
> categorize vhost user messages to 2 types: non-vring specific messages,
> which should be sent only once, and vring specific messages, which should
> be sent per queue.
> 
> Here I introduced a helper function vhost_user_one_time_request(), which
> lists following messages as non-vring specific messages:
> 
>         VHOST_USER_SET_OWNER
>         VHOST_USER_RESET_DEVICE
>         VHOST_USER_SET_MEM_TABLE
>         VHOST_USER_GET_QUEUE_NUM
> 
> For above messages, we simply ignore them when they are not sent the first
> time.
> 
> Signed-off-by: Nikolay Nikolaev <address@hidden>
> Signed-off-by: Changchun Ouyang <address@hidden>
> Signed-off-by: Yuanhan Liu <address@hidden>
> 
> ---

Just focusing on the interface portions:

> +++ b/qapi-schema.json
> @@ -2480,12 +2480,16 @@
>  #
>  # @vhostforce: #optional vhost on for non-MSIX virtio guests (default: 
> false).
>  #
> +# @queues: #optional number of queues to be created for multiqueue vhost-user
> +#          (default: 1) (Since 2.5)
> +#
>  # Since 2.1
>  ##
>  { 'struct': 'NetdevVhostUserOptions',
>    'data': {
>      'chardev':        'str',
> -    '*vhostforce':    'bool' } }
> +    '*vhostforce':    'bool',
> +    '*queues':        'int' } }
>  

Discoverable via introspection, and should work with the patches from
Zoltan and me that get QMP netdev_add converted over to qapi.

Interface is good to go.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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