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Mon, 28 Jul 2025 04:03:10 -0700 (PDT) From: Pavel Begunkov To: Jakub Kicinski , netdev@vger.kernel.org Cc: asml.silence@gmail.com, io-uring@vger.kernel.org, Eric Dumazet , Willem de Bruijn , Paolo Abeni , andrew+netdev@lunn.ch, horms@kernel.org, davem@davemloft.net, sdf@fomichev.me, almasrymina@google.com, dw@davidwei.uk, michael.chan@broadcom.com, dtatulea@nvidia.com, ap420073@gmail.com Subject: [RFC v1 01/22] docs: ethtool: document that rx_buf_len must control payload lengths Date: Mon, 28 Jul 2025 12:04:05 +0100 Message-ID: X-Mailer: git-send-email 2.49.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: io-uring@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 we have 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 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/networking/ethtool-netlink.rst index b6e9af4d0f1b..eaa9c17a3cb1 100644 --- a/Documentation/networking/ethtool-netlink.rst +++ b/Documentation/networking/ethtool-netlink.rst @@ -957,7 +957,6 @@ Kernel checks that requested ring sizes do not exceed limits reported by driver. Driver may impose additional constraints and may not support all attributes. - ``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 @@ -971,6 +970,11 @@ 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. +``ETHTOOL_A_RINGS_RX_BUF_LEN`` controls the size of the buffer chunks driver +uses to receive packets. If the device uses different memory polls for headers +and payload this setting may control the size of the header buffers but must +control the size of the payload buffers. + CHANNELS_GET ============ -- 2.49.0