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Message-ID: <ZNEI9IqMOfH+smbo@lincoln> Date: Mon, 7 Aug 2023 17:08:36 +0200 From: Larysa Zaremba <larysa.zaremba@...el.com> To: Jakub Kicinski <kuba@...nel.org> CC: Willem de Bruijn <willemdebruijn.kernel@...il.com>, Alexei Starovoitov <alexei.starovoitov@...il.com>, bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, David Ahern <dsahern@...il.com>, Willem de Bruijn <willemb@...gle.com>, Jesper Dangaard Brouer <brouer@...hat.com>, Anatoly Burakov <anatoly.burakov@...el.com>, Alexander Lobakin <alexandr.lobakin@...el.com>, Magnus Karlsson <magnus.karlsson@...il.com>, Maryam Tahhan <mtahhan@...hat.com>, <xdp-hints@...-project.net>, Network Development <netdev@...r.kernel.org>, Simon Horman <simon.horman@...igine.com> Subject: Re: [PATCH bpf-next v4 12/21] xdp: Add checksum hint On Mon, Jul 31, 2023 at 09:43:22AM -0700, Jakub Kicinski wrote: > On Sun, 30 Jul 2023 09:13:02 -0400 Willem de Bruijn wrote: > > > > This levels business is an unfortunate side effect of > > > > CHECKSUM_UNNECESSARY. For a packet with multiple checksum fields, what > > > > does the boolean actually mean? With these levels, at least that is > > > > well defined: the first N checksum fields. > > > > > > If I understand this correctly this is intel specific feature that > > > other NICs don't have. skb layer also doesn't have such concept. > > > The driver should say CHECKSUM_UNNECESSARY when it's sure > > > or don't pretend that it checks the checksum and just say NONE. > > > > I did not know how much this was used, but quick grep for non constant > > csum_level shows devices from at least six vendors. > > I thought it was a legacy thing from early VxLAN days. > We used to leave outer UDP csum as 0 before LCO, and therefore couldn't > convert outer to COMPLETE, so inner could not be offloaded/validated. > Should not be all that relevant today. Sorry for the delayed response. Thanks a lot for this feedback, it became a gateway to deepen my understanding of checksumming in kernel pretty significantly.
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