netdev - Re: [PATCH net-next 3/4] net: add code for TCP fraglist GRO

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Date: Fri, 26 Apr 2024 10:14:06 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Felix Fietkau <nbd@....name>, netdev@...r.kernel.org, Eric Dumazet
 <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Jakub
 Kicinski <kuba@...nel.org>, David Ahern <dsahern@...nel.org>
Cc: willemdebruijn.kernel@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 3/4] net: add code for TCP fraglist GRO

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.
> 
> Signed-off-by: Felix Fietkau <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(-)
> 
> 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);
>  
>  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_head *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;
>  }
>  
> -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 = NULL;
>  	struct sk_buff *p;
> @@ -289,6 +290,7 @@ struct sk_buff *tcp_gro_receive(struct list_head *head, struct sk_buff *skb)
>  	len = skb_gro_len(skb);
>  	flags = tcp_flag_word(th);
>  
> +	NAPI_GRO_CB(skb)->is_flist = 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 *head, struct sk_buff *skb)
>  found:
>  	/* Include the IP ID check below from the inner most IP hdr */
>  	flush = NAPI_GRO_CB(p)->flush;
> +	flush |= fraglist != NAPI_GRO_CB(p)->is_flist;
>  	flush |= (__force int)(flags & TCP_FLAG_CWR);
>  	flush |= (__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 *head, struct sk_buff *skb)
>  	flush |= (ntohl(th2->seq) + skb_gro_len(p)) ^ ntohl(th->seq);
>  	flush |= skb_cmp_decrypted(p, skb);
>  
> +	if (fraglist) {
> +		flush |= (__force int)(flags ^ tcp_flag_word(th2));

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


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

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

> +		flush |= NAPI_GRO_CB(p)->count >= 64;
> +
> +		if (flush || skb_gro_receive_list(p, skb))
> +			mss = 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