diff options
author | Kuniyuki Iwashima <kuniyu@amazon.com> | 2023-08-04 01:45:51 +0300 |
---|---|---|
committer | Jakub Kicinski <kuba@kernel.org> | 2023-08-05 04:28:36 +0300 |
commit | d0f2b7a9ca0a1a89d65ee145815f89b54b7f977f (patch) | |
tree | d54f7f55d7471785786c753611cfc19d97baa34c /net/ipv4/tcp_output.c | |
parent | f4bf467883f210d0bfbe784fffca52887de147fb (diff) | |
download | linux-d0f2b7a9ca0a1a89d65ee145815f89b54b7f977f.tar.xz |
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 <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20230803224552.69398-2-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv4/tcp_output.c')
-rw-r--r-- | net/ipv4/tcp_output.c | 5 |
1 files changed, 0 insertions, 5 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 51d8638d4b4c..c5412ee77fc8 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -3741,11 +3741,6 @@ static void tcp_connect_init(struct sock *sk) if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_timestamps)) tp->tcp_header_len += TCPOLEN_TSTAMP_ALIGNED; -#ifdef CONFIG_TCP_MD5SIG - if (tp->af_specific->md5_lookup(sk, sk)) - tp->tcp_header_len += TCPOLEN_MD5SIG_ALIGNED; -#endif - /* If user gave his TCP_MAXSEG, record it to clamp */ if (tp->rx_opt.user_mss) tp->rx_opt.mss_clamp = tp->rx_opt.user_mss; |