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AJvYcCW2QqVfvvdlDMYjUqmRjC5kdRVVE7bFMiC+/YwbwMZ0MFttooClJdEw0da3msd8rJ3S8w5MlqW1G7E=@vger.kernel.org X-Gm-Message-State: AOJu0YzL+XPjH+dCyyTSP5O9uNUR6WvvvkRRlbVn+p5qYy2IkHEo/4ST 114OtmGAg3kH6sB7KmP52K1nB/H00iTVyHPqkzA9LpvfNB6uwreOKrtodnc0V6djnapi14ydW73 4gFoJ+Z2aOXEMLoW7W93bXU6KIf6FWQ+PL2JxaEhD X-Gm-Gg: ASbGncuV/NVht8ZL9xsJp1GjTOWuzMqVPl2THVykHD7+Pz2Q3mHvJ3YAfhh5RdSREIL 8icLC+B3qDCHg7rxfdPDhJI6hmf/noHbv2NmZI1L/Gr6KFuDf5j5ThN1f3XWpu9VtBzE4t0GGDM Iq9gvOFUcI5rBz0/BehhhcfPEPl/N8vlLOf9ap2hOWRoNx9vid17bWAr/zarbEcabY20y2tUQNj JLUvFcNHsPfAep4ObujbarhrQ== X-Google-Smtp-Source: AGHT+IE/rVuZ9SCIHg1gU7wHZFKJcVFlbis3SdAosQsMQXAAs3D+JvW5TH6jC+V2oisrZbfPgFfUQfa4iF740e0XHhA= X-Received: by 2002:a05:620a:1915:b0:7e9:f820:2b32 with SMTP id af79cd13be357-7ea0972ad73mr237461685a.39.1755781472346; Thu, 21 Aug 2025 06:04:32 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250815083930.10547-1-chia-yu.chang@nokia-bell-labs.com> <20250815083930.10547-15-chia-yu.chang@nokia-bell-labs.com> In-Reply-To: <20250815083930.10547-15-chia-yu.chang@nokia-bell-labs.com> From: Eric Dumazet Date: Thu, 21 Aug 2025 06:04:20 -0700 X-Gm-Features: Ac12FXyJZ2QzT9xkYMMFg0cMwGaeSy-IVq_aPmJhAwN18-ZLuJFS365DtCRetGA Message-ID: Subject: Re: [PATCH v15 net-next 14/14] tcp: accecn: try to fit AccECN option with SACK To: chia-yu.chang@nokia-bell-labs.com Cc: pabeni@redhat.com, linux-doc@vger.kernel.org, corbet@lwn.net, horms@kernel.org, dsahern@kernel.org, kuniyu@amazon.com, bpf@vger.kernel.org, netdev@vger.kernel.org, dave.taht@gmail.com, jhs@mojatatu.com, kuba@kernel.org, stephen@networkplumber.org, xiyou.wangcong@gmail.com, jiri@resnulli.us, davem@davemloft.net, andrew+netdev@lunn.ch, donald.hunter@gmail.com, ast@fiberby.net, liuhangbin@gmail.com, shuah@kernel.org, linux-kselftest@vger.kernel.org, ij@kernel.org, ncardwell@google.com, koen.de_schepper@nokia-bell-labs.com, g.white@cablelabs.com, ingemar.s.johansson@ericsson.com, mirja.kuehlewind@ericsson.com, cheshire@apple.com, rs.ietf@gmx.at, Jason_Livingood@comcast.com, vidhi_goel@apple.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, Aug 15, 2025 at 1:40=E2=80=AFAM = wrote: > > From: Chia-Yu Chang > > As SACK blocks tend to eat all option space when there are > many holes, it is useful to compromise on sending many SACK > blocks in every ACK and attempt to fit the AccECN option > there by reducing the number of SACK blocks. However, it will > never go below two SACK blocks because of the AccECN option. > > As the AccECN option is often not put to every ACK, the space > hijack is usually only temporary. Depending on the reuqired > AccECN fields (can be either 3, 2, 1, or 0, cf. Table 5 in > AccECN spec) and the NOPs used for alignment of other > TCP options, up to two SACK blocks will be reduced. Please > find below tables for more details: > > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+ > | Number of | Required | Remaining | Number of | Final | > | SACK | AccECN | option | reduced | number of | > | blocks | fields | spaces | SACK blocks | SACK blocks | > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+ > | x (<=3D2) | 0 to 3 | any | 0 | x | > +-----------+----------+-----------+-------------+-------------+ > | 3 | 0 | any | 0 | 3 | > | 3 | 1 | <4 | 1 | 2 | > | 3 | 1 | >=3D4 | 0 | 3 | > | 3 | 2 | <8 | 1 | 2 | > | 3 | 2 | >=3D8 | 0 | 3 | > | 3 | 3 | <12 | 1 | 2 | > | 3 | 3 | >=3D12 | 0 | 3 | > +-----------+----------+-----------+-------------+-------------+ > | y (>=3D4) | 0 | any | 0 | y | > | y (>=3D4) | 1 | <4 | 1 | y-1 | > | y (>=3D4) | 1 | >=3D4 | 0 | y | > | y (>=3D4) | 2 | <8 | 1 | y-1 | > | y (>=3D4) | 2 | >=3D8 | 0 | y | > | y (>=3D4) | 3 | <4 | 2 | y-2 | > | y (>=3D4) | 3 | <12 | 1 | y-1 | > | y (>=3D4) | 3 | >=3D12 | 0 | y | > +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D+ > It is unclear if this chart takes into account the TCP TS option ? Can you clarify this point ?