[PATCH net-next v3 02/23] docs: ethtool: document that rx_buf_len must control payload lengths
From: Pavel Begunkov <asml.silence@gmail.com>
Date: 2025-08-18 13:56:35
Also in:
io-uring, lkml
Subsystem:
documentation, networking [ethtool], networking [general], the rest · Maintainers:
Jonathan Corbet, Andrew Lunn, Jakub Kicinski, "David S. Miller", Eric Dumazet, Paolo Abeni, Linus Torvalds
From: Jakub Kicinski <kuba@kernel.org> 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 <kuba@kernel.org> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- 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 ab20c644af24..cae372f719d1 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 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
@@ -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. +``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 ============
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