netdev - Re: Optimizing instruction-cache, more packets at each stage

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 21 Jan 2016 14:49:25 +0200
From:	Or Gerlitz <gerlitz.or@...il.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
Cc:	Tom Herbert <tom@...bertland.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Alexander Duyck <alexander.duyck@...il.com>,
	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Daniel Borkmann <borkmann@...earbox.net>,
	Marek Majkowski <marek@...udflare.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Florian Westphal <fw@...len.de>,
	Paolo Abeni <pabeni@...hat.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Amir Vadai <amirva@...il.com>,
	Matan Barak <matanb@...lanox.com>
Subject: Re: Optimizing instruction-cache, more packets at each stage

On Thu, Jan 21, 2016 at 1:27 PM, Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
> On Wed, 20 Jan 2016 15:27:38 -0800 Tom Herbert <tom@...bertland.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.