netdev - Re: [PATCH bpf-next v7 00/13] net-timestamp: bpf extension to equip applications transparently

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Message-ID: <2706706c-3d85-4f43-ad91-d04bbb4f2b92@linux.dev>
Date: Mon, 3 Feb 2025 18:27:26 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, dsahern@...nel.org, willemdebruijn.kernel@...il.com,
 willemb@...gle.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, horms@...nel.org, bpf@...r.kernel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next v7 00/13] net-timestamp: bpf extension to equip
 applications transparently

On 1/28/25 12:46 AM, Jason Xing wrote:
> "Timestamping is key to debugging network stack latency. With
> SO_TIMESTAMPING, bugs that are otherwise incorrectly assumed to be
> network issues can be attributed to the kernel." This is extracted
> from the talk "SO_TIMESTAMPING: Powering Fleetwide RPC Monitoring"
> addressed by Willem de Bruijn at netdevconf 0x17).
> 
> There are a few areas that need optimization with the consideration of
> easier use and less performance impact, which I highlighted and mainly
> discussed at netconf 2024 with Willem de Bruijn and John Fastabend:
> uAPI compatibility, extra system call overhead, and the need for
> application modification. I initially managed to solve these issues
> by writing a kernel module that hooks various key functions. However,
> this approach is not suitable for the next kernel release. Therefore,
> a BPF extension was proposed. During recent period, Martin KaFai Lau
> provides invaluable suggestions about BPF along the way. Many thanks
> here!
> 
> In this series, I only support foundamental codes and tx for TCP.

*fundamental*.

May be just "only tx time stamping for TCP is supported..."

> This approach mostly relies on existing SO_TIMESTAMPING feature, users
> only needs to pass certain flags through bpf_setsocktopt() to a separate
> tsflags. Please see the last selftest patch in this series.
> 
> After this series, we could step by step implement more advanced
> functions/flags already in SO_TIMESTAMPING feature for bpf extension.

Patch 1-4 and 6-11 can use an extra "bpf:" tag in the subject line. Patch 13 
should be "selftests/bpf:" instead of "bpf:" in the subject.

Please revisit the commit messages of this patch set to check for outdated 
comments from the earlier revisions. I may have missed some of them.

Overall, it looks close. I will review at your replies later.

Willem, could you also take a look? Thanks.