Subject: Re: [RFC net-next 17/22] netdev: add support for setting rx-buf-len per queue

From: Stanislav Fomichev <[email-masked]>
Date: Tue, 22 Apr 2025 09:15:59 -0700

On 04/21, Jakub Kicinski wrote:
> Zero-copy APIs increase the cost of buffer management. They also extend
> this cost to user space applications which may be used to dealing with
> much larger buffers. Allow setting rx-buf-len per queue, devices with
> HW-GRO support can commonly fill buffers up to 32k (or rather 64k - 1
> but that's not a power of 2..)
> 
> The implementation adds a new option to the netdev netlink, rather
> than ethtool. The NIC-wide setting lives in ethtool ringparams so
> one could argue that we should be extending the ethtool API.
> OTOH netdev API is where we already have queue-get, and it's how
> zero-copy applications bind memory providers.
> 
> Signed-off-by: Jakub Kicinski <[email-masked]>
> ---
>  Documentation/netlink/specs/netdev.yaml | 15 ++++
>  include/net/netdev_queues.h             |  5 ++
>  include/net/netlink.h                   | 19 +++++
>  include/uapi/linux/netdev.h             |  2 +
>  net/core/netdev-genl-gen.h              |  1 +
>  tools/include/uapi/linux/netdev.h       |  2 +
>  net/core/netdev-genl-gen.c              | 15 ++++
>  net/core/netdev-genl.c                  | 92 +++++++++++++++++++++++++
>  net/core/netdev_config.c                | 16 +++++
>  9 files changed, 167 insertions(+)
> 
> diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
> index f5e0750ab71d..b0dfa970ee83 100644
> --- a/Documentation/netlink/specs/netdev.yaml
> +++ b/Documentation/netlink/specs/netdev.yaml
> @@ -324,6 +324,10 @@ name: netdev
>          doc: XSK information for this queue, if any.
>          type: nest
>          nested-attributes: xsk-info
> +      -
> +        name: rx-buf-len
> +        doc: Per-queue configuration of ETHTOOL_A_RINGS_RX_BUF_LEN.
> +        type: u32
>    -
>      name: qstats
>      doc: |
> @@ -743,6 +747,17 @@ name: netdev
>              - defer-hard-irqs
>              - gro-flush-timeout
>              - irq-suspend-timeout
> +    -
> +      name: queue-set
> +      doc: Set per-queue configurable options.
> +      attribute-set: queue
> +      do:
> +        request:
> +          attributes:
> +            - ifindex
> +            - type
> +            - id
> +            - rx-buf-len

Do we want some guidance going forward on what belongs to queue-set
vs napi-set? (mostly) HW settings for the queue-set and (mostly) SW
settings for (serving the queues) in napi-set?