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Message-ID: <ce46af97c03471c64f1fcff27c41e65ca82dd151.camel@redhat.com>
Subject: Re: [PATCH net-next 3/4] net: add code for TCP fraglist GRO
From: Paolo Abeni <pabeni@redhat.com>
To: Felix Fietkau <nbd@nbd.name>, netdev@vger.kernel.org, Eric Dumazet
 <edumazet@google.com>, "David S. Miller" <davem@davemloft.net>, Jakub
 Kicinski <kuba@kernel.org>, David Ahern <dsahern@kernel.org>
Cc: willemdebruijn.kernel@gmail.com, linux-kernel@vger.kernel.org
Date: Fri, 26 Apr 2024 10:14:06 +0200
In-Reply-To: <20240424180458.56211-4-nbd@nbd.name>
References: <20240424180458.56211-1-nbd@nbd.name>
	 <20240424180458.56211-4-nbd@nbd.name>
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On Wed, 2024-04-24 at 20:04 +0200, Felix Fietkau wrote:
> This implements fraglist GRO similar to how it's handled in UDP, however
> no functional changes are added yet. The next change adds a heuristic for
> using fraglist GRO instead of regular GRO.
>=20
> Signed-off-by: Felix Fietkau <nbd@nbd.name>
> ---
>  include/net/tcp.h        |  3 ++-
>  net/ipv4/tcp_offload.c   | 29 +++++++++++++++++++++++++++--
>  net/ipv6/tcpv6_offload.c | 11 ++++++++++-
>  3 files changed, 39 insertions(+), 4 deletions(-)
>=20
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index b935e1ae4caf..875cda53a7c9 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -2194,7 +2194,8 @@ void tcp_v4_destroy_sock(struct sock *sk);
> =20
>  struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
>  				netdev_features_t features);
> -struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *=
skb);
> +struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *=
skb,
> +				bool fraglist);
>  INDIRECT_CALLABLE_DECLARE(int tcp4_gro_complete(struct sk_buff *skb, int=
 thoff));
>  INDIRECT_CALLABLE_DECLARE(struct sk_buff *tcp4_gro_receive(struct list_h=
ead *head, struct sk_buff *skb));
>  INDIRECT_CALLABLE_DECLARE(int tcp6_gro_complete(struct sk_buff *skb, int=
 thoff));
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 06dbb2e2b2f3..6294e7a5c099 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -252,7 +252,8 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb,
>  	return segs;
>  }
> =20
> -struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *=
skb)
> +struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *=
skb,
> +				bool fraglist)
>  {
>  	struct sk_buff *pp =3D NULL;
>  	struct sk_buff *p;
> @@ -289,6 +290,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *hea=
d, struct sk_buff *skb)
>  	len =3D skb_gro_len(skb);
>  	flags =3D tcp_flag_word(th);
> =20
> +	NAPI_GRO_CB(skb)->is_flist =3D fraglist;
>  	list_for_each_entry(p, head, list) {
>  		if (!NAPI_GRO_CB(p)->same_flow)
>  			continue;
> @@ -308,6 +310,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *hea=
d, struct sk_buff *skb)
>  found:
>  	/* Include the IP ID check below from the inner most IP hdr */
>  	flush =3D NAPI_GRO_CB(p)->flush;
> +	flush |=3D fraglist !=3D NAPI_GRO_CB(p)->is_flist;
>  	flush |=3D (__force int)(flags & TCP_FLAG_CWR);
>  	flush |=3D (__force int)((flags ^ tcp_flag_word(th2)) &
>  		  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));
> @@ -341,6 +344,19 @@ struct sk_buff *tcp_gro_receive(struct list_head *he=
ad, struct sk_buff *skb)
>  	flush |=3D (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq);
>  	flush |=3D skb_cmp_decrypted(p, skb);
> =20
> +	if (fraglist) {
> +		flush |=3D (__force int)(flags ^ tcp_flag_word(th2));

Don't we have this check already a few lines above?


> +		flush |=3D skb->ip_summed !=3D p->ip_summed;
> +		flush |=3D skb->csum_level !=3D p->csum_level;
> +		flush |=3D !pskb_may_pull(skb, skb_gro_offset(skb));

Why we need this check? The earlier skb_gro_may_pull() should ensure
that, right?

> +		flush |=3D NAPI_GRO_CB(p)->count >=3D 64;
> +
> +		if (flush || skb_gro_receive_list(p, skb))
> +			mss =3D 1;
> +
> +		goto out_check_final;

TCP flags processing needs some care. You need to propagate the current
packets flag to the old one, and update the older packet csum
accordingly.

Cheers,

Paolo