From: Stanislav Fomichev <sdf@google.com>
To: Menglong Dong <menglong8.dong@gmail.com>
Cc: andrii@kernel.org, ast@kernel.org, daniel@iogearbox.net,
martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev,
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: Tue, 2 Jan 2024 10:11:34 -0800 [thread overview]
Message-ID: <ZZRR1q1JrJMD1lAy@google.com> (raw)
In-Reply-To: <20231229081409.1276386-1-menglong8.dong@gmail.com>
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.
>
> In the first patch, we make skb->csum readable and writable, and we make
> skb->ip_summed readable. For now, for tc only. With these 2 fields, we
> don't need to call bpf helpers for csum update any more.
>
> In the second patch, we add some testcases for the read/write testing for
> skb->csum and skb->ip_summed.
>
> If this series is acceptable, we can define the inlined functions for csum
> update in libbpf in the next step.
One downside of exposing those as __sk_buff fields is that all this
skb internal csum stuff now becomes a UAPI. And I'm not sure we want
that :-) Should we add a lightweight kfunc to reset the fields instead?
Or will it still have an unacceptable overhead?
next prev parent reply other threads:[~2024-01-02 18:11 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 ` Stanislav Fomichev [this message]
2024-01-03 0:52 ` [PATCH bpf-next 0/2] bpf: add csum/ip_summed fields to __sk_buff Martin KaFai Lau
2024-01-03 2:54 ` Menglong Dong
2024-01-03 3:55 ` Yonghong Song
2024-01-03 6:03 ` Menglong Dong
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