netdev - Re: Performance question: af_packet with bpf filter vs TX path skb

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Message-ID: <b9336a67-c337-ae86-2604-81368dcdfbac@bernat.ch>
Date: Sat, 5 Aug 2023 10:54:52 +0200
From: Vincent Bernat <vincent@...nat.ch>
To: Maciej Żenczykowski <maze@...gle.com>,
 Jesper Dangaard Brouer <hawk@...nel.org>
Cc: Eric Dumazet <edumazet@...gle.com>, Linux NetDev
 <netdev@...r.kernel.org>, Pengtao He <hepengtao@...omi.com>,
 Willem Bruijn <willemb@...gle.com>, Stanislav Fomichev <sdf@...gle.com>,
 Xiao Ma <xiaom@...gle.com>, Patrick Rohr <prohr@...gle.com>,
 Alexei Starovoitov <ast@...nel.org>, Dave Tucker <datucker@...hat.com>,
 Marek Majkowski <marek@...udflare.com>
Subject: Re: Performance question: af_packet with bpf filter vs TX path
 skb_clone

On 2023-08-03 10:46, Maciej Żenczykowski wrote:
> I think a fair number of these can get by with non-ETH_P_ALL (for 
> example ETH_P_LLDP), or can use a different socket for RX (where you can 
> choose to not see your own TX packets) and transmit via ETH_P_NONE (btw. 
> that constant should really exist and be equal to 0)

Hey!

For lldpd, I was using ETH_P_LLDP in the past, but there was cases where 
packets are not received, notably when an interface is enslaved by an 
Open vSwitch. See: 
https://github.com/lldpd/lldpd/commit/8b50be7f61ad20ebae15372a509f7e778da2cc6f

This may have been fixed, but this kind of differences between ETH_P_ALL 
and ETH_P_LLDP makes it difficult to trust ETH_P_LLDP to do the right 
thing as it will work for most people but a few edge cases may appear.