From: Menglong Dong <menglong8.dong@gmail.com>
To: Yonghong Song <yonghong.song@linux.dev>
Cc: Martin KaFai Lau <martin.lau@linux.dev>,
Stanislav Fomichev <sdf@google.com>,
andrii@kernel.org, ast@kernel.org, daniel@iogearbox.net,
song@kernel.org, john.fastabend@gmail.com, kpsingh@kernel.org,
haoluo@google.com, jolsa@kernel.org, davem@davemloft.net,
edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
mykolal@fb.com, shuah@kernel.org, horms@kernel.org,
dhowells@redhat.com, linyunsheng@huawei.com,
aleksander.lobakin@intel.com, joannelkoong@gmail.com,
laoar.shao@gmail.com, kuifeng@meta.com, bjorn@rivosinc.com,
linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
netdev@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [PATCH bpf-next 0/2] bpf: add csum/ip_summed fields to __sk_buff
Date: Wed, 3 Jan 2024 14:03:02 +0800 [thread overview]
Message-ID: <CADxym3aYT6ftPMFiuMSiTpNEYpvPz1p3rEtK6bX2_N=BreXOzQ@mail.gmail.com> (raw)
In-Reply-To: <4fa8ae9d-11fd-4728-83bd-848cb22952e7@linux.dev>
On Wed, Jan 3, 2024 at 11:55 AM Yonghong Song <yonghong.song@linux.dev> wrote:
>
>
> On 1/2/24 6:54 PM, Menglong Dong wrote:
> > On Wed, Jan 3, 2024 at 8:52 AM Martin KaFai Lau <martin.lau@linux.dev> wrote:
> >> On 1/2/24 10:11 AM, Stanislav Fomichev wrote:
> >>> On 12/29, Menglong Dong wrote:
> >>>> For now, we have to call some helpers when we need to update the csum,
> >>>> such as bpf_l4_csum_replace, bpf_l3_csum_replace, etc. These helpers are
> >>>> not inlined, which causes poor performance.
> >>>>
> >>>> In fact, we can define our own csum update functions in BPF program
> >>>> instead of bpf_l3_csum_replace, which is totally inlined and efficient.
> >>>> However, we can't do this for bpf_l4_csum_replace for now, as we can't
> >>>> update skb->csum, which can cause skb->csum invalid in the rx path with
> >>>> CHECKSUM_COMPLETE mode.
> >>>>
> >>>> What's more, we can't use the direct data access and have to use
> >>>> skb_store_bytes() with the BPF_F_RECOMPUTE_CSUM flag in some case, such
> >>>> as modifing the vni in the vxlan header and the underlay udp header has
> >>>> no checksum.
> >> There is bpf_csum_update(), does it work?
> >> A helper call should be acceptable comparing with the csum calculation itself.
> > Yeah, this helper works in this case! Now we miss the last
> > piece for the tx path: ip_summed. We need to know if it is
> > CHECKSUM_PARTIAL to decide if we should update the
> > csum in the packet. In the tx path, the csum in the L4 is the
> > pseudo header only if skb->ip_summed is CHECKSUM_PARTIAL.
> >
> > Maybe we can introduce a lightweight kfunc to get its
> > value? Such as bpf_skb_csum_mode(). As we need only call
> > it once, there shouldn't be overhead on it.
>
> You don't need kfunc, you can do checking like
> struct sk_buff *kskb = bpf_cast_to_kern_ctx(skb);
> if (kskb->ip_summed == CHECKSUM_PARTIAL) ...
> ...
>
Great, this is exactly what I need! Thanks~
prev parent reply other threads:[~2024-01-03 6:03 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-29 8:14 [PATCH bpf-next 0/2] bpf: add csum/ip_summed fields to __sk_buff Menglong Dong
2023-12-29 8:14 ` [PATCH bpf-next 1/2] " Menglong Dong
2023-12-29 8:14 ` [PATCH bpf-next 2/2] testcases/bpf: add testcases for skb->csum to ctx_skb.c Menglong Dong
2024-01-02 18:11 ` [PATCH bpf-next 0/2] bpf: add csum/ip_summed fields to __sk_buff Stanislav Fomichev
2024-01-03 0:52 ` Martin KaFai Lau
2024-01-03 2:54 ` Menglong Dong
2024-01-03 3:55 ` Yonghong Song
2024-01-03 6:03 ` Menglong Dong [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CADxym3aYT6ftPMFiuMSiTpNEYpvPz1p3rEtK6bX2_N=BreXOzQ@mail.gmail.com' \
--to=menglong8.dong@gmail.com \
--cc=aleksander.lobakin@intel.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bjorn@rivosinc.com \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=davem@davemloft.net \
--cc=dhowells@redhat.com \
--cc=edumazet@google.com \
--cc=haoluo@google.com \
--cc=horms@kernel.org \
--cc=joannelkoong@gmail.com \
--cc=john.fastabend@gmail.com \
--cc=jolsa@kernel.org \
--cc=kpsingh@kernel.org \
--cc=kuba@kernel.org \
--cc=kuifeng@meta.com \
--cc=laoar.shao@gmail.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linyunsheng@huawei.com \
--cc=martin.lau@linux.dev \
--cc=mykolal@fb.com \
--cc=netdev@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=sdf@google.com \
--cc=shuah@kernel.org \
--cc=song@kernel.org \
--cc=yonghong.song@linux.dev \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).