cilium的一个vxlan性能优化记录

vxlan UDP 数据包的 GRO aggregation处理是在vxlan驱动处理流程中进行的，物理口收到vxlan udp报文后没有做GRO aggregation，原因是udp header的csum为0，导致如下代码中，udp_gro_receive 函数中，(NAPI_GRO_CB(skb)->csum_cnt == 0 && !NAPI_GRO_CB(skb)->csum_valid)) 为true 退出了函数。

本文kernel: 4.18。新版本内核（5.4+）相关修改已经合入。

struct sk_buff **udp_gro_receive(struct sk_buff **head, struct sk_buff *skb,
                 struct udphdr *uh, udp_lookup_t lookup)
{
    struct sk_buff *p, **pp = NULL;
    struct udphdr *uh2;
    unsigned int off = skb_gro_offset(skb);
    int flush = 1;
    struct sock *sk;

    if (NAPI_GRO_CB(skb)->encap_mark ||
        (skb->ip_summed != CHECKSUM_PARTIAL &&
         NAPI_GRO_CB(skb)->csum_cnt == 0 &&
         !NAPI_GRO_CB(skb)->csum_valid))
        goto out;
     
     
......     
     
out:
    skb_gro_flush_final(skb, pp, flush);
    return pp;
}
EXPORT_SYMBOL(udp_gro_receive);

测试记录：

[...]
swapper 0 [008] 731.946506: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100400 len=1500 (1)
swapper 0 [008] 731.946507: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100200 len=1500
swapper 0 [008] 731.946507: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101100 len=1500
swapper 0 [008] 731.946508: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101700 len=1500
swapper 0 [008] 731.946508: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101b00 len=1500
swapper 0 [008] 731.946508: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100600 len=1500
swapper 0 [008] 731.946508: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100f00 len=1500
swapper 0 [008] 731.946509: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100a00 len=1500
swapper 0 [008] 731.946516: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100500 len=1500
swapper 0 [008] 731.946516: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100700 len=1500
swapper 0 [008] 731.946516: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101d00 len=1500 (2)
swapper 0 [008] 731.946517: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101000 len=1500
swapper 0 [008] 731.946517: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101c00 len=1500
swapper 0 [008] 731.946517: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101400 len=1500
swapper 0 [008] 731.946518: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100e00 len=1500
swapper 0 [008] 731.946518: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497101600 len=1500
swapper 0 [008] 731.946521: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff966497100800 len=774
swapper 0 [008] 731.946530: net:netif_receive_skb: dev=test_vxlan skbaddr=0xffff966497100400 len=14032 (1)
swapper 0 [008] 731.946530: net:netif_receive_skb: dev=test_vxlan skbaddr=0xffff966497101d00 len=9112 (2)
[...]

#netperf -H 10.55.10.4 -t TCP_STREAM -l 20
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.55.10.4 () port 0 AF_INET : demo
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec

87380 16384 16384 20.01 13129.24

考虑在csum为0时，跳前在物理口完成GRO aggregation，对吞吐量提升很大，修改如下：

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index b76c48efd37ee..c5b4b586570fe 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -526,7 +526,7 @@ struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
    }
 
    if (!sk || NAPI_GRO_CB(skb)->encap_mark ||
-       (skb->ip_summed != CHECKSUM_PARTIAL &&
+       (uh->check && skb->ip_summed != CHECKSUM_PARTIAL &&
         NAPI_GRO_CB(skb)->csum_cnt == 0 &&
         !NAPI_GRO_CB(skb)->csum_valid) ||
        !udp_sk(sk)->gro_receive)

测试记录：

[...]
swapper 0 [026] 521.862641: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff93ab0d479000 len=11286 (1)
swapper 0 [026] 521.862643: net:netif_receive_skb: dev=test_vxlan skbaddr=0xffff93ab0d479000 len=11236 (1)
swapper 0 [026] 521.862650: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff93ab0d478500 len=2898 (2)
swapper 0 [026] 521.862650: net:netif_receive_skb: dev=enp10s0f0 skbaddr=0xffff93ab0d479f00 len=8490 (3)
swapper 0 [026] 521.862653: net:netif_receive_skb: dev=test_vxlan skbaddr=0xffff93ab0d478500 len=2848 (2)
swapper 0 [026] 521.862653: net:netif_receive_skb: dev=test_vxlan skbaddr=0xffff93ab0d479f00 len=8440 (3)
[...]

# netperf -H 10.55.10.4 -t TCP_STREAM -l 20
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.55.10.4 () port 0 AF_INET : demo
Recv Send Send
Socket Socket Message Elapsed
Size Size Size Time Throughput
bytes bytes bytes secs. 10^6bits/sec

87380 16384 16384 20.01 24576.53