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Date: Thu, 25 Apr 2024 17:26:04 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Felix Fietkau <nbd@....name>
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 v2 net-next v2 5/5] net: add heuristic for enabling TCP
fraglist GRO
On Thu, Apr 25, 2024 at 5:04 PM 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 | 48 +++++++++++++++++++++++++++++++++++++
> net/ipv6/tcpv6_offload.c | 51 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 99 insertions(+)
>
> diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c
> index 520fd425ab19..3bb96a110402 100644
> --- a/net/ipv4/tcp_offload.c
> +++ b/net/ipv4/tcp_offload.c
> @@ -405,6 +405,52 @@ 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)
> +{
> + const struct iphdr *iph = skb_gro_network_header(skb);
I do not think loading iph before all skb_gro_header() and
skb_gro_header_slow() calls is wise.
pskb_may_pull() can re-allocate skb->head
> + struct net *net = dev_net(skb->dev);
> + unsigned int off, hlen, thlen;
> + struct sk_buff *p;
> + struct tcphdr *th;
> + struct sock *sk;
> + int iif, sdif;
> +
> + if (!(skb->dev->features & NETIF_F_GRO_FRAGLIST))
> + return;
> +
> + off = skb_gro_offset(skb);
> + hlen = off + sizeof(*th);
> + th = skb_gro_header(skb, hlen, off);
> + if (unlikely(!th))
> + return;
> +
> + thlen = th->doff * 4;
> + if (thlen < sizeof(*th))
> + return;
> +
> + hlen = off + thlen;
> + if (!skb_gro_may_pull(skb, hlen)) {
> + th = skb_gro_header_slow(skb, hlen, off);
> + if (unlikely(!th))
> + return;
> + }
> +
> + p = tcp_gro_lookup(head, th);
> + if (p) {
> + NAPI_GRO_CB(skb)->is_flist = NAPI_GRO_CB(p)->is_flist;
> + return;
> + }
> +
> + inet_get_iif_sdif(skb, &iif, &sdif);
> + sk = __inet_lookup_established(net, net->ipv4.tcp_death_row.hashinfo,
> + iph->saddr, th->source,
> + iph->daddr, ntohs(th->dest),
> + iif, sdif);
> + NAPI_GRO_CB(skb)->is_flist = !sk;
> + if (sk)
> + sock_put(sk);
> +}
> +
> INDIRECT_CALLABLE_SCOPE
> struct sk_buff *tcp4_gro_receive(struct list_head *head, struct sk_buff *skb)
> {
> @@ -416,6 +462,8 @@ struct sk_buff *tcp4_gro_receive(struct list_head *head, struct sk_buff *skb)
> return NULL;
> }
>
I would probably pull the whole TCP header here, before calling
tcp4_check_fraglist_gro(head, skb)
and no longer do this twice from tcp4_check_fraglist_gro() and tcp_gro_receive()
Perhaps define a new inline helper, that will be called from
tcp4_gro_receive() and tcp6_gro_receive(),
and not anymore from tcp_gro_receive()
static inline struct tcphdr *tcp_gro_pull_header(...)
{
....
off = skb_gro_offset(skb);
hlen = off + sizeof(*th);
th = skb_gro_header(skb, hlen, off);
if (unlikely(!th))
return NULL;
thlen = th->doff * 4;
if (thlen < sizeof(*th))
return NULL;
hlen = off + thlen;
if (!skb_gro_may_pull(skb, hlen))
th = skb_gro_header_slow(skb, hlen, off);
return th;
}
> + tcp4_check_fraglist_gro(head, skb);
> +
> return tcp_gro_receive(head, skb);
> }
>
> diff --git a/net/ipv6/tcpv6_offload.c b/net/ipv6/tcpv6_offload.c
> index c97d55cf036f..7948420dcad0 100644
> --- a/net/ipv6/tcpv6_offload.c
> +++ b/net/ipv6/tcpv6_offload.c
> @@ -7,12 +7,61 @@
> */
> #include <linux/indirect_call_wrapper.h>
> #include <linux/skbuff.h>
> +#include <net/inet6_hashtables.h>
> #include <net/gro.h>
> #include <net/protocol.h>
> #include <net/tcp.h>
> #include <net/ip6_checksum.h>
> #include "ip6_offload.h"
>
> +static void tcp6_check_fraglist_gro(struct list_head *head, struct sk_buff *skb)
> +{
> +#if IS_ENABLED(CONFIG_IPV6)
> + const struct ipv6hdr *hdr = skb_gro_network_header(skb);
> + struct net *net = dev_net(skb->dev);
> + unsigned int off, hlen, thlen;
> + struct sk_buff *p;
> + struct tcphdr *th;
> + struct sock *sk;
> + int iif, sdif;
> +
> + if (!(skb->dev->features & NETIF_F_GRO_FRAGLIST))
> + return;
> +
> + off = skb_gro_offset(skb);
> + hlen = off + sizeof(*th);
> + th = skb_gro_header(skb, hlen, off);
> + if (unlikely(!th))
> + return;
> +
> + thlen = th->doff * 4;
> + if (thlen < sizeof(*th))
> + return;
> +
> + hlen = off + thlen;
> + if (!skb_gro_may_pull(skb, hlen)) {
> + th = skb_gro_header_slow(skb, hlen, off);
> + if (unlikely(!th))
> + return;
> + }
> +
> + p = tcp_gro_lookup(head, th);
> + if (p) {
> + NAPI_GRO_CB(skb)->is_flist = NAPI_GRO_CB(p)->is_flist;
> + return;
> + }
> +
> + inet6_get_iif_sdif(skb, &iif, &sdif);
> + sk = __inet6_lookup_established(net, net->ipv4.tcp_death_row.hashinfo,
> + &hdr->saddr, th->source,
> + &hdr->daddr, ntohs(th->dest),
> + iif, sdif);
> + NAPI_GRO_CB(skb)->is_flist = !sk;
> + if (sk)
> + sock_put(sk);
> +#endif /* IS_ENABLED(CONFIG_IPV6) */
> +}
> +
> INDIRECT_CALLABLE_SCOPE
> struct sk_buff *tcp6_gro_receive(struct list_head *head, struct sk_buff *skb)
> {
> @@ -24,6 +73,8 @@ struct sk_buff *tcp6_gro_receive(struct list_head *head, struct sk_buff *skb)
> return NULL;
> }
>
> + tcp6_check_fraglist_gro(head, skb);
> +
> return tcp_gro_receive(head, skb);
> }
>
> --
> 2.44.0
>
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