netdev - Re: [RFC net-next 01/22] docs: ethtool: document that rx_buf

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Message-ID: <dca8f379-92f1-4d7b-89ff-f71f43343e23@davidwei.uk>
Date: Tue, 22 Apr 2025 09:19:16 -0700
From: David Wei <dw@...idwei.uk>
To: Jakub Kicinski <kuba@...nel.org>, davem@...emloft.net
Cc: netdev@...r.kernel.org, edumazet@...gle.com, pabeni@...hat.com,
 andrew+netdev@...n.ch, horms@...nel.org, donald.hunter@...il.com,
 sdf@...ichev.me, almasrymina@...gle.com, asml.silence@...il.com,
 ap420073@...il.com, jdamato@...tly.com, dtatulea@...dia.com,
 michael.chan@...adcom.com
Subject: Re: [RFC net-next 01/22] docs: ethtool: document that rx_buf_len must
 control payload lengths

On 2025-04-21 15:28, Jakub Kicinski wrote:
> 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@...nel.org>
> ---
>  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

pools

> +and payload this setting may control the size of the header buffers but must
> +control the size of the payload buffers.
> +
>  CHANNELS_GET
>  ============
>