netdev - Re: [PATCH v3 net-next v3 6/6] net: add heuristic for enabling TCP fraglist GRO

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Message-ID: <b7c9f59b-682d-4444-9906-58704f0f0359@nbd.name>
Date: Fri, 26 Apr 2024 11:21:13 +0200
From: Felix Fietkau <nbd@....name>
To: Eric Dumazet <edumazet@...gle.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
 David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, willemdebruijn.kernel@...il.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 net-next v3 6/6] net: add heuristic for enabling TCP
 fraglist GRO

On 26.04.24 09:32, Eric Dumazet wrote:
> On Fri, Apr 26, 2024 at 8:51 AM Felix Fietkau <nbd@....name> wrote:
>>
>> When forwarding TCP after GRO, software segmentation is very expensive,
>> especially when the checksum needs to be recalculated.
>> One case where that's currently unavoidable is when routing packets over
>> PPPoE. Performance improves significantly when using fraglist GRO
>> implemented in the same way as for UDP.
>>
>> When NETIF_F_GRO_FRAGLIST is enabled, perform a lookup for an established
>> socket in the same netns as the receiving device. While this may not
>> cover all relevant use cases in multi-netns configurations, it should be
>> good enough for most configurations that need this.
>>
>> Here's a measurement of running 2 TCP streams through a MediaTek MT7622
>> device (2-core Cortex-A53), which runs NAT with flow offload enabled from
>> one ethernet port to PPPoE on another ethernet port + cake qdisc set to
>> 1Gbps.
>>
>> rx-gro-list off: 630 Mbit/s, CPU 35% idle
>> rx-gro-list on:  770 Mbit/s, CPU 40% idle
>>
>> Signe-off-by: Felix Fietkau <nbd@....name>
>> ---
>>  net/ipv4/tcp_offload.c   | 30 ++++++++++++++++++++++++++++++
>>  net/ipv6/tcpv6_offload.c | 33 +++++++++++++++++++++++++++++++++
>>  2 files changed, 63 insertions(+)
>>
>> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
>> index ee5403760775..2ae83f4394dc 100644
>> --- a/net/ipv4/tcp_offload.c
>> +++ b/net/ipv4/tcp_offload.c
>> @@ -406,6 +406,34 @@ void tcp_gro_complete(struct sk_buff *skb)
>>  }
>>  EXPORT_SYMBOL(tcp_gro_complete);
>>
>> +static void tcp4_check_fraglist_gro(struct list_head *head, struct sk_buff *skb,
>> +                                   struct tcphdr *th)
>> +{
>> +       const struct iphdr *iph = skb_gro_network_header(skb);
>> +       struct net *net = dev_net(skb->dev);
> 
> Could you defer the initializations of iph and net after the
> NETIF_F_GRO_FRAGLIST check ?
> 
> dev_net() has an implicit READ_ONCE() ...

Will do, thanks.

- Felix