linux-kernel - Re: [PATCH net-next v3 2/5] net: gro: only merge packets with incrementing or fixed outer ids

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Message-ID: <d986135a-d0ee-4878-9fc2-958f35d569da@redhat.com>
Date: Fri, 22 Aug 2025 10:26:44 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Richard Gobert <richardbgobert@...il.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 horms@...nel.org, corbet@....net, saeedm@...dia.com, tariqt@...dia.com,
 mbloch@...dia.com, leon@...nel.org, ecree.xilinx@...il.com,
 dsahern@...nel.org, ncardwell@...gle.com, kuniyu@...gle.com,
 shuah@...nel.org, sdf@...ichev.me, aleksander.lobakin@...el.com,
 florian.fainelli@...adcom.com, willemdebruijn.kernel@...il.com,
 alexander.duyck@...il.com, linux-kernel@...r.kernel.org,
 linux-net-drivers@....com
Subject: Re: [PATCH net-next v3 2/5] net: gro: only merge packets with
 incrementing or fixed outer ids

On 8/21/25 9:30 AM, Richard Gobert wrote:
> @@ -442,29 +442,26 @@ static inline __wsum ip6_gro_compute_pseudo(const struct sk_buff *skb,
>  }
>  
>  static inline int inet_gro_flush(const struct iphdr *iph, const struct iphdr *iph2,
> -				 struct sk_buff *p, bool outer)
> +				 struct sk_buff *p, bool inner)
>  {
>  	const u32 id = ntohl(*(__be32 *)&iph->id);
>  	const u32 id2 = ntohl(*(__be32 *)&iph2->id);
>  	const u16 ipid_offset = (id >> 16) - (id2 >> 16);
>  	const u16 count = NAPI_GRO_CB(p)->count;
>  	const u32 df = id & IP_DF;
> -	int flush;
>  
>  	/* All fields must match except length and checksum. */
> -	flush = (iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF));
> -
> -	if (flush | (outer && df))
> -		return flush;
> +	if ((iph->ttl ^ iph2->ttl) | (iph->tos ^ iph2->tos) | (df ^ (id2 & IP_DF)))
> +		return true;
>  
>  	/* When we receive our second frame we can make a decision on if we
>  	 * continue this flow as an atomic flow with a fixed ID or if we use
>  	 * an incrementing ID.
>  	 */
>  	if (count == 1 && df && !ipid_offset)
> -		NAPI_GRO_CB(p)->ip_fixedid = true;
> +		NAPI_GRO_CB(p)->ip_fixedid |= 1 << inner;
>  
> -	return ipid_offset ^ (count * !NAPI_GRO_CB(p)->ip_fixedid);
> +	return ipid_offset ^ (count * !(NAPI_GRO_CB(p)->ip_fixedid & (1 << inner)));
>  }
>  
>  static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr *iph2)
> @@ -478,28 +475,30 @@ static inline int ipv6_gro_flush(const struct ipv6hdr *iph, const struct ipv6hdr
>  }
>  
>  static inline int __gro_receive_network_flush(const void *th, const void *th2,
> -					      struct sk_buff *p, const u16 diff,
> -					      bool outer)
> +					      struct sk_buff *p, bool inner)
>  {
> -	const void *nh = th - diff;
> -	const void *nh2 = th2 - diff;
> +	const void *nh, *nh2;
> +	int off, diff;
> +
> +	off = skb_transport_offset(p);
> +	diff = off - NAPI_GRO_CB(p)->network_offsets[inner];
> +	nh = th - diff;
> +	nh2 = th2 - diff;
>  
>  	if (((struct iphdr *)nh)->version == 6)
>  		return ipv6_gro_flush(nh, nh2);
>  	else
> -		return inet_gro_flush(nh, nh2, p, outer);
> +		return inet_gro_flush(nh, nh2, p, inner);
>  }
>  
>  static inline int gro_receive_network_flush(const void *th, const void *th2,
>  					    struct sk_buff *p)
>  {
> -	const bool encap_mark = NAPI_GRO_CB(p)->encap_mark;
> -	int off = skb_transport_offset(p);
>  	int flush;
>  
> -	flush = __gro_receive_network_flush(th, th2, p, off - NAPI_GRO_CB(p)->network_offset, encap_mark);
> -	if (encap_mark)
> -		flush |= __gro_receive_network_flush(th, th2, p, off - NAPI_GRO_CB(p)->inner_network_offset, false);
> +	flush = __gro_receive_network_flush(th, th2, p, false);
> +	if (NAPI_GRO_CB(p)->encap_mark)
> +		flush |= __gro_receive_network_flush(th, th2, p, true);

Minor nit: I'm under the (unverified) impression that the old syntax
could help the compiler generating better code. What about storing the
diff in a local variable:

	int diff;

	diff = skb_transport_offset(p) - NAPI_GRO_CB(p)->network_offset;
	flush = __gro_receive_network_flush(th, th2, diff, false);
	if (NAPI_GRO_CB(p)->encap_mark)
		flush |= __gro_receive_network_flush(th, th2, diff, true);

?

/P