netdev - Re: xdp generic default option

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Date:   Wed, 19 Aug 2020 16:39:47 +0200
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, andriin@...com
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        David Miller <davem@...emloft.net>, ast@...nel.org
Subject: Re: xdp generic default option

Lorenzo Bianconi <lorenzo@...nel.org> writes:

> Hi Andrii,
>
> working on xdp multi-buff I figured out now xdp generic is the default choice
> if not specified by userspace. In particular after commit 7f0a838254bd
> ("bpf, xdp: Maintain info on attached XDP BPF programs in net_device"), running
> the command below, XDP will run in generic mode even if the underlay driver
> support XDP in native mode:
>
> $ip link set dev eth0 xdp obj prog.o
> $ip link show dev eth0
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 xdpgeneric qdisc mq state UP mode DEFAULT
>    group default qlen 1024
>    link/ether f0:ad:4e:09:6b:57 brd ff:ff:ff:ff:ff:ff
>    prog/xdp id 1 tag 3b185187f1855c4c jited

Yeah, defaulting to xdpgeneric is not a good idea (and a change in
behaviour; I get native mode on the same command on a 5.8 kernel)...

-Toke