linux-kernel - Re: [PATCH v2 net-next v2 3/5] net: add code for TCP fraglist GRO

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Message-ID: <662a746130c38_1e1a1629422@willemb.c.googlers.com.notmuch>
Date: Thu, 25 Apr 2024 11:18:57 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Felix Fietkau <nbd@....name>, 
 netdev@...r.kernel.org, 
 Eric Dumazet <edumazet@...gle.com>, 
 "David S. Miller" <davem@...emloft.net>, 
 David Ahern <dsahern@...nel.org>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>
Cc: willemdebruijn.kernel@...il.com, 
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net-next v2 3/5] net: add code for TCP fraglist GRO

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>
> ---
>  net/ipv4/tcp_offload.c   | 22 ++++++++++++++++++++++
>  net/ipv6/tcpv6_offload.c |  9 +++++++++
>  2 files changed, 31 insertions(+)
> 
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index e455f884190c..68157130c264 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -336,6 +336,19 @@ 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 (NAPI_GRO_CB(p)->is_flist) {
> +		flush |= (__force int)(flags ^ tcp_flag_word(th2));

What is the purpose of this check, given the existing check above

        flush |= (__force int)((flags ^ tcp_flag_word(th2)) &
                  ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH));

> +		flush |= skb->ip_summed != p->ip_summed;
> +		flush |= skb->csum_level != p->csum_level;
> +		flush |= !pskb_may_pull(skb, skb_gro_offset(skb));
> +		flush |= NAPI_GRO_CB(p)->count >= 64;
> +
> +		if (flush || skb_gro_receive_list(p, skb))
> +			mss = 1;
> +
> +		goto out_check_final;
> +	}
> +
>  	if (flush || skb_gro_receive(p, skb)) {
>  		mss = 1;
>  		goto out_check_final;
> @@ -402,6 +415,15 @@ INDIRECT_CALLABLE_SCOPE int tcp4_gro_complete(struct sk_buff *skb, int thoff)
>  	const struct iphdr *iph = ip_hdr(skb);
>  	struct tcphdr *th = tcp_hdr(skb);
>  
> +	if (NAPI_GRO_CB(skb)->is_flist) {
> +		skb_shinfo(skb)->gso_type |= SKB_GSO_FRAGLIST | SKB_GSO_TCPV4;
> +		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
> +
> +		__skb_incr_checksum_unnecessary(skb);
> +
> +		return 0;
> +	}
> +
>  	th->check = ~tcp_v4_check(skb->len - thoff, iph->saddr,
>  				  iph->daddr, 0);
>  
> diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
> index b3b8e1f6b92a..c97d55cf036f 100644
> --- a/net/ipv6/tcpv6_offload.c
> +++ b/net/ipv6/tcpv6_offload.c
> @@ -32,6 +32,15 @@ INDIRECT_CALLABLE_SCOPE int tcp6_gro_complete(struct sk_buff *skb, int thoff)
>  	const struct ipv6hdr *iph = ipv6_hdr(skb);
>  	struct tcphdr *th = tcp_hdr(skb);
>  
> +	if (NAPI_GRO_CB(skb)->is_flist) {
> +		skb_shinfo(skb)->gso_type |= SKB_GSO_FRAGLIST | SKB_GSO_TCPV6;
> +		skb_shinfo(skb)->gso_segs = NAPI_GRO_CB(skb)->count;
> +
> +		__skb_incr_checksum_unnecessary(skb);
> +
> +		return 0;
> +	}
> +
>  	th->check = ~tcp_v6_check(skb->len - thoff, &iph->saddr,
>  				  &iph->daddr, 0);
>  	skb_shinfo(skb)->gso_type |= SKB_GSO_TCPV6;
> -- 
> 2.44.0
>