[ovs-dev] [PATCH] ofproto: Avoid user->kernel->user round-trip for many controller actions.

[Martin Casado]

> On Wed, Aug 4, 2010 at 2:09 PM, Ben Pfaff <blp at nicira.com 
> <mailto:blp at nicira.com>> wrote:
>
>     +        copy = ofpbuf_new(DPIF_RECV_MSG_PADDING + sizeof(struct
>     odp_msg)
>     +                          + packet->size);
>     +        ofpbuf_reserve(copy, DPIF_RECV_MSG_PADDING);
>     +        msg = ofpbuf_put_uninit(copy, sizeof *msg);
>     +        msg->type = _ODPL_ACTION_NR;
>     +        msg->length = sizeof(struct odp_msg) + packet->size;
>     +        msg->port = in_port;
>     +        msg->reserved = 0;
>     +        msg->arg = actions[0].controller.arg;
>     +        ofpbuf_put(copy, packet->data, packet->size);
>
>
> How common is it that sending to the controller is the only action?  
> It seems like that might be a fairly common scenario here.  If so, it 
> would be ideal if we could avoid copying the packet an additional time 
> here.  I don't know if it is worth it though seeing as this is already 
> a fairly narrow use case (first packet to the controller).
For some applications this is used fairly heavily.  If the optimization 
is not too onerous, probably worthwhile adding.