linux-kernel - Re: [PATCH v3 net-next v3 3/6] net: add code for TCP fraglist GRO

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Date: Fri, 26 Apr 2024 11:41:55 +0200
From: Felix Fietkau <nbd@....name>
To: Paolo Abeni <pabeni@...hat.com>, 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>
Cc: willemdebruijn.kernel@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net-next v3 3/6] net: add code for TCP fraglist GRO

On 26.04.24 10:21, Paolo Abeni wrote:
> On Fri, 2024-04-26 at 08:51 +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>
>> ---
>>  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 c493e95e09a5..ffd6b7a4163a 100644
>> --- a/net/ipv4/tcp_offload.c
>> +++ b/net/ipv4/tcp_offload.c
>> @@ -332,6 +332,19 @@ 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));
>> +		flush |= skb->ip_summed != p->ip_summed;
>> +		flush |= skb->csum_level != p->csum_level;
>> +		flush |= !pskb_may_pull(skb, skb_gro_offset(skb));
> 
> I'm sorry, I'm lagging behind. I think the TCP flags handling here is
> correct - preserving the original ones should work.
> 
> The question a made WRT 2 above checks being non necessary/redundant:
> 
> 		flush |= (__force int)(flags ^ tcp_flag_word(th2));

This one is not redundant, because the earlier flags check includes this 
part: & ~(TCP_FLAG_CWR | TCP_FLAG_FIN | TCP_FLAG_PSH))

> 		flush |= !pskb_may_pull(skb, skb_gro_offset(skb));

This one looks like a redundant leftover, I will remove it in the next 
version.

Thanks,

- Felix