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Sat, 19 Sep 2026 11:12:17 -0700 (PDT) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Sat, 19 Sep 2026 18:12:17 +0000 Message-Id: Cc: , , "Jason Xing" Subject: Re: [PATCH RFC net-next 0/9] net: BPF Timestamping 2.0 for TCP From: "Alexei Starovoitov" To: "Jason Xing" , , , , , , , X-Mailer: aerc 0.17.0 References: <20260919143732.11772-1-kerneljasonxing@gmail.com> In-Reply-To: <20260919143732.11772-1-kerneljasonxing@gmail.com> On Sat Sep 19, 2026 at 2:37 PM UTC, Jason Xing wrote: > From: Jason Xing > > Greeting, > > It's BPF Timestamping 2.0 that aims to observe the packet latency > more efficiently and simply for different protocols. The current > series is only focused on TCP protocol. > > At Netdev 0x1a/Netconf 2026, the history, background, motivation and > rough implementation of the feature were exhaustively introduced[1]. > > History > =3D=3D=3D=3D=3D=3D=3D > - In 2009, Patrick Ohly implemented the basic infrastructure > - In 2014, Willem de Bruijn enhanced the TCP latency observation > - In 2024, Jason Xing proposed its lightweight BPF version > Detailed slides from 28 to 32 [1]. > > Background > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D > Even though BPF Timetamping 1.0 is comparatively low-overhead, > transparent, it's still complicated due to a few points inherited > from the design: > - Inflexible/fixed reporting phases (qdisc/driver/ack) > When we confirm the issue arises from the kernel by using attribution > ability of timestamping feature, we need to further minimize the scope > until the issue is fixed. That means, we then have to resort to write > a few complex BPF progs with the similar functionalities (like skb > level tag) which should not happen. > - Not enough low-overhead > Serving the sensitive applications, an always-on latency observation > platform should mitigate the self-impact as much as possible. As we > can conclude from BPF Timestamping selftests, there are some blocking > and time-consuming points like where reading/writing BPF maps happen > in the extremely hot paths. > - Minor flaws > There are a few minor flaws inherited from the initial design, like > missing tagging the last packet[2][3][4]. All these "issues" sound minor and on their own do not warrant new uapi. This RFC don't even have an example of how it could be used end-to-end. So soft nack from me for now. pw-bot: cr