linux-kernel - Re: [PATCH net-next v3 1/8] net: gro: decouple GRO from the NAPI layer

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Message-ID: <87ikqdobk7.fsf@toke.dk>
Date: Fri, 17 Jan 2025 13:43:36 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>, Lorenzo Bianconi
 <lorenzo@...nel.org>, Daniel Xu <dxu@...uu.xyz>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, John Fastabend <john.fastabend@...il.com>, Jesper
 Dangaard Brouer <hawk@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, netdev@...r.kernel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 1/8] net: gro: decouple GRO from the NAPI layer

Alexander Lobakin <aleksander.lobakin@...el.com> writes:

> In fact, these two are not tied closely to each other. The only
> requirements to GRO are to use it in the BH context and have some
> sane limits on the packet batches, e.g. NAPI has a limit of its
> budget (64/8/etc.).
> Move purely GRO fields into a new tagged group, &gro_node. Embed it
> into &napi_struct and adjust all the references. napi_id doesn't
> really belong to GRO, but:
>
> 1. struct gro_node has a 4-byte padding at the end anyway. If you
>    leave napi_id outside, struct napi_struct takes additional 8 bytes
>    (u32 napi_id + another 4-byte padding).
> 2. gro_receive_skb() uses it to mark skbs. We don't want to split it
>    into two functions or add an `if`, as this would be less efficient,
>    but we need it to be NAPI-independent. The current approach doesn't
>    change anything for NAPI-backed GROs; for standalone ones (which
>    are less important currently), the embedded napi_id will be just
>    zero => no-op.
>
> Three Ethernet drivers use napi_gro_flush() not really meant to be
> exported, so move it to <net/gro.h> and add that include there.
> napi_gro_receive() is used in more than 100 drivers, keep it
> in <linux/netdevice.h>.
> This does not make GRO ready to use outside of the NAPI context
> yet.
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> Tested-by: Daniel Xu <dxu@...uu.xyz>

Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>