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Mon, 13 Oct 2025 07:53:23 -0700 (PDT) From: Pavel Begunkov To: netdev@vger.kernel.org Cc: Andrew Lunn , Jakub Kicinski , davem@davemloft.net, Eric Dumazet , Paolo Abeni , Simon Horman , Donald Hunter , Michael Chan , Pavan Chebbi , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Joshua Washington , Harshitha Ramamurthy , Jian Shen , Salil Mehta , Jijie Shao , Sunil Goutham , Geetha sowjanya , Subbaraya Sundeep , hariprasad , Bharat Bhushan , Saeed Mahameed , Tariq Toukan , Mark Bloch , Leon Romanovsky , Alexander Duyck , kernel-team@meta.com, Ilias Apalodimas , Joe Damato , David Wei , Willem de Bruijn , Mina Almasry , Pavel Begunkov , Breno Leitao , Dragos Tatulea , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-rdma@vger.kernel.org, Jonathan Corbet Subject: [PATCH net-next v4 02/24] docs: ethtool: document that rx_buf_len must control payload lengths Date: Mon, 13 Oct 2025 15:54:04 +0100 Message-ID: X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@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" From: Jakub Kicinski Document the semantics of the rx_buf_len ethtool ring param. Clarify its meaning in case of HDS, where driver may have two separate buffer pools. The various zero-copy TCP Rx schemes suffer from memory management overhead. Specifically applications aren't too impressed with the number of 4kB buffers they have to juggle. Zero-copy TCP makes most sense with larger memory transfers so using 16kB or 32kB buffers (with the help of HW-GRO) feels more natural. Signed-off-by: Jakub Kicinski Reviewed-by: Mina Almasry Signed-off-by: Pavel Begunkov --- Documentation/networking/ethtool-netlink.rst | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/Documentation/networking/ethtool-netlink.rst b/Documentation/n= etworking/ethtool-netlink.rst index b270886c5f5d..392a359a9cab 100644 --- a/Documentation/networking/ethtool-netlink.rst +++ b/Documentation/networking/ethtool-netlink.rst @@ -966,7 +966,6 @@ Kernel checks that requested ring sizes do not exceed l= imits reported by driver. Driver may impose additional constraints and may not support all attributes. =20 - ``ETHTOOL_A_RINGS_CQE_SIZE`` specifies the completion queue event size. Completion queue events (CQE) are the events posted by NIC to indicate the completion status of a packet when the packet is sent (like send success or @@ -980,6 +979,11 @@ completion queue size can be adjusted in the driver if= CQE size is modified. header / data split feature. If a received packet size is larger than this threshold value, header and data will be split. =20 +``ETHTOOL_A_RINGS_RX_BUF_LEN`` controls the size of the buffers driver +uses to receive packets. If the device uses different buffer pools for +headers and payload (due to HDS, HW-GRO etc.) this setting must +control the size of the payload buffers. + CHANNELS_GET =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =20 --=20 2.49.0