On Wed, Apr 24, 2024 at 8:05 PM Felix Fietkau <[email protected]> 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 <[email protected]>
> ---
> net/ipv4/tcp_offload.c | 45 ++++++++++++++++++++++++++++++++++++++-
> net/ipv6/tcpv6_offload.c | 46 +++++++++++++++++++++++++++++++++++++++-
> 2 files changed, 89 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 6294e7a5c099..f987e2d8423a 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -404,6 +404,49 @@ void tcp_gro_complete(struct sk_buff *skb)
> }
> EXPORT_SYMBOL(tcp_gro_complete);
>
> +static bool tcp4_check_fraglist_gro(struct sk_buff *skb)
> +{
> + const struct iphdr *iph = skb_gro_network_header(skb);
> + struct net *net = dev_net(skb->dev);
> + unsigned int off, hlen, thlen;
> + struct tcphdr *th;
> + struct sock *sk;
> + int iif, sdif;
> +
> + if (!(skb->dev->features & NETIF_F_GRO_FRAGLIST))
> + return false;
> +
> + inet_get_iif_sdif(skb, &iif, &sdif);
> +
> + off = skb_gro_offset(skb);
> + hlen = off + sizeof(*th);
> + th = skb_gro_header(skb, hlen, off);
> + if (unlikely(!th))
> + return false;
> +
> + thlen = th->doff * 4;
> + if (thlen < sizeof(*th))
> + return false;
> +
> + hlen = off + thlen;
> + if (!skb_gro_may_pull(skb, hlen)) {
> + th = skb_gro_header_slow(skb, hlen, off);
> + if (unlikely(!th))
> + return false;
> + }
> +
> + sk = __inet_lookup_established(net, net->ipv4.tcp_death_row.hashinfo,
> + iph->saddr, th->source,
> + iph->daddr, ntohs(th->dest),
> + iif, sdif);
Presumably all this could be done only for the first skb/segment of a GRO train.
We could store the fraglist in a single bit in NAPI_GRO_CB(skb) ?
GRO does a full tuple evaluation, we can trust it.
On 24.04.24 20:23, Eric Dumazet wrote:
> On Wed, Apr 24, 2024 at 8:05 PM Felix Fietkau <[email protected]> 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 <[email protected]>
>> ---
>> net/ipv4/tcp_offload.c | 45 ++++++++++++++++++++++++++++++++++++++-
>> net/ipv6/tcpv6_offload.c | 46 +++++++++++++++++++++++++++++++++++++++-
>> 2 files changed, 89 insertions(+), 2 deletions(-)
>>
>> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
>> index 6294e7a5c099..f987e2d8423a 100644
>> --- a/net/ipv4/tcp_offload.c
>> +++ b/net/ipv4/tcp_offload.c
>> @@ -404,6 +404,49 @@ void tcp_gro_complete(struct sk_buff *skb)
>> }
>> EXPORT_SYMBOL(tcp_gro_complete);
>>
>> +static bool tcp4_check_fraglist_gro(struct sk_buff *skb)
>> +{
>> + const struct iphdr *iph = skb_gro_network_header(skb);
>> + struct net *net = dev_net(skb->dev);
>> + unsigned int off, hlen, thlen;
>> + struct tcphdr *th;
>> + struct sock *sk;
>> + int iif, sdif;
>> +
>> + if (!(skb->dev->features & NETIF_F_GRO_FRAGLIST))
>> + return false;
>> +
>> + inet_get_iif_sdif(skb, &iif, &sdif);
>> +
>> + off = skb_gro_offset(skb);
>> + hlen = off + sizeof(*th);
>> + th = skb_gro_header(skb, hlen, off);
>> + if (unlikely(!th))
>> + return false;
>> +
>> + thlen = th->doff * 4;
>> + if (thlen < sizeof(*th))
>> + return false;
>> +
>> + hlen = off + thlen;
>> + if (!skb_gro_may_pull(skb, hlen)) {
>> + th = skb_gro_header_slow(skb, hlen, off);
>> + if (unlikely(!th))
>> + return false;
>> + }
>> +
>> + sk = __inet_lookup_established(net, net->ipv4.tcp_death_row.hashinfo,
>> + iph->saddr, th->source,
>> + iph->daddr, ntohs(th->dest),
>> + iif, sdif);
>
> Presumably all this could be done only for the first skb/segment of a GRO train.
>
> We could store the fraglist in a single bit in NAPI_GRO_CB(skb) ?
>
> GRO does a full tuple evaluation, we can trust it.
I will look into that, thanks.
- Felix