From d0f2b7a9ca0a1a89d65ee145815f89b54b7f977f Mon Sep 17 00:00:00 2001 From: Kuniyuki Iwashima Date: Thu, 3 Aug 2023 15:45:51 -0700 Subject: tcp: Disable header prediction for MD5 flow. TCP socket saves the minimum required header length in tcp_header_len of struct tcp_sock, and later the value is used in __tcp_fast_path_on() to generate a part of TCP header in tcp_sock(sk)->pred_flags. In tcp_rcv_established(), if the incoming packet has the same pattern with pred_flags, we enter the fast path and skip full option parsing. The MD5 option is parsed in tcp_v[46]_rcv(), so we need not parse it again later in tcp_rcv_established() unless other options exist. We add TCPOLEN_MD5SIG_ALIGNED to tcp_header_len in two paths to avoid the slow path. For passive open connections with MD5, we add TCPOLEN_MD5SIG_ALIGNED to tcp_header_len in tcp_create_openreq_child() after 3WHS. On the other hand, we do it in tcp_connect_init() for active open connections. However, the value is overwritten while processing SYN+ACK or crossed SYN in tcp_rcv_synsent_state_process(). These two cases will have the wrong value in pred_flags and never go into the fast path. We could update tcp_header_len in tcp_rcv_synsent_state_process(), but a test with slightly modified netperf which uses MD5 for each flow shows that the slow path is actually a bit faster than the fast path. On c5.4xlarge EC2 instance (16 vCPU, 32 GiB mem) $ for i in {1..10}; do ./super_netperf $(nproc) -H localhost -l 10 -- -m 256 -M 256; done Avg of 10 * 36e68eadd303 : 10.376 Gbps * all fast path : 10.374 Gbps (patch v2, See Link) * all slow path : 10.394 Gbps The header prediction is not worth adding complexity for MD5, so let's disable it for MD5. Link: https://lore.kernel.org/netdev/20230803042214.38309-1-kuniyu@amazon.com/ Signed-off-by: Kuniyuki Iwashima Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/20230803224552.69398-2-kuniyu@amazon.com Signed-off-by: Jakub Kicinski --- net/ipv4/tcp_minisocks.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'net/ipv4/tcp_minisocks.c') diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c index c8f2aa003387..ddba3b67f7c8 100644 --- a/net/ipv4/tcp_minisocks.c +++ b/net/ipv4/tcp_minisocks.c @@ -570,8 +570,6 @@ struct sock *tcp_create_openreq_child(const struct sock *sk, newtp->tsoffset = treq->ts_off; #ifdef CONFIG_TCP_MD5SIG newtp->md5sig_info = NULL; /*XXX*/ - if (treq->af_specific->req_md5_lookup(sk, req_to_sk(req))) - newtp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; #endif if (skb->len >= TCP_MSS_DEFAULT + newtp->tcp_header_len) newicsk->icsk_ack.last_seg_size = skb->len - newtp->tcp_header_len; -- cgit v1.2.3