On Thu, Jan 21, 2016 at 1:27 PM, Jesper Dangaard Brouer
<bro...@redhat.com> wrote:
> On Wed, 20 Jan 2016 15:27:38 -0800 Tom Herbert <t...@herbertland.com> wrote:
>
>> eth_type_trans touches headers
>
> True, the eth_type_trans() call in the driver is a major bottleneck,
> because it touch the packet header and happens very early in the driver.
>
> In my experiments, where I extract several packet before calling
> napi_gro_receive(), and I also delay calling eth_type_trans(). Most of
> my speedup comes from this trick, as the prefetch() now that enough
> time.
>
> while ((skb = __skb_dequeue(&rx_skb_list)) != NULL) {
> skb->protocol = eth_type_trans(skb, rq->netdev);
> napi_gro_receive(cq->napi, skb);
> }
>
> What is the HW could provide the info we need in the descriptor?!?
>
>
> eth_type_trans() does two things:
>
> 1) determine skb->protocol
> 2) setup skb->pkt_type = PACKET_{BROADCAST,MULTICAST,OTHERHOST}
>
> Could the HW descriptor deliver the "proto", or perhaps just some bits
> on the most common proto's?
>
> The skb->pkt_type don't need many bits. And I bet the HW already have
> the information. The BROADCAST and MULTICAST indication are easy. The
> PACKET_OTHERHOST, can be turned around, by instead set a PACKET_HOST
> indication, if the eth->h_dest match the devices dev->dev_addr (else a
> SW compare is required).
>
> Is that doable in hardware?
As I wrote earlier, for determination of the eth-type HWs can do what you ask
here and more.
Protocol being IP or not (and only then you look in the data) you could
get I guess from many NICs, e.g if the NIC sets PKT_HASH_TYPE_L4
or PKT_HASH_TYPE_L3 then we know it's an IP packets and only if
we don't see this indication we look into the data.
As for pkt_type we can use NIC steering HW to provide us a tag saying if
it was our broadcast, other multicast or "our" unicast.
Or.
