netdev - Re: [PATCH bpf-next v11 00/12] net-timestamp: bpf extension to equip applications transparently

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Message-ID: <035d99ac-0f39-444d-bf2a-68d46f0e22a2@linux.dev>
Date: Fri, 14 Feb 2025 12:42:59 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>, willemdebruijn.kernel@...il.com
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, dsahern@...nel.org, 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 v11 00/12] net-timestamp: bpf extension to equip
 applications transparently

On 2/13/25 5:00 PM, 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!
> 
> This series adds the BPF networking timestamping infrastructure through
> reusing most of the tx timestamping callback that is currently enabled
> by the SO_TIMESTAMPING.. This series also adds TX timestamping support
> for TCP. The RX timestamping and UDP support will be added in the future.
> 
> ---
> v10
> Link: https://lore.kernel.org/all/20250212061855.71154-1-kerneljasonxing@gmail.com/
> 1. rename hwts with hwtimestamp
> 2. use subtest and pid filter in selftest
> 3. use 'tcb->txstamp_ack |= TSTAMP_ACK_SK'

Overall looks good. I only have two minor comments.

Willem, can you also take another look and ack if it looks good to you? Thanks.