Commit 3acf3ec3 authored Sep 27, 2016 by Lawrence Brakmo Committed by David S. Miller Sep 28, 2016

tcp: Change txhash on every SYN and RTO retransmit



The current code changes txhash (flowlables) on every retransmitted
SYN/ACK, but only after the 2nd retransmitted SYN and only after
tcp_retries1 RTO retransmits.

With this patch:
1) txhash is changed with every SYN retransmits
2) txhash is changed with every RTO.

The result is that we can start re-routing around failed (or very
congested paths) as soon as possible. Otherwise application health
checks may fail and the connection may be terminated before we start
to change txhash.

v4: Removed sysctl, txhash is changed for all RTOs
v3: Removed text saying default value of sysctl is 0 (it is 100)
v2: Added sysctl documentation and cleaned code

Tested with packetdrill tests

Signed-off-by: Lawrence Brakmo <brakmo@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent fa5effe7

net/ipv4/tcp_timer.c

+4 −0

Original line number	Original line	Diff line number	Diff line
	@@ -192,6 +192,8 @@ static int tcp_write_timeout(struct sock *sk)
	if (tp->syn_data && icsk->icsk_retransmits == 1)		if (tp->syn_data && icsk->icsk_retransmits == 1)
	NET_INC_STATS(sock_net(sk),		NET_INC_STATS(sock_net(sk),
	LINUX_MIB_TCPFASTOPENACTIVEFAIL);		LINUX_MIB_TCPFASTOPENACTIVEFAIL);
			} else if (!tp->syn_data && !tp->syn_fastopen) {
			sk_rethink_txhash(sk);
	}		}
	retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;		retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;
	syn_set = true;		syn_set = true;
	@@ -213,6 +215,8 @@ static int tcp_write_timeout(struct sock *sk)
	tcp_mtu_probing(icsk, sk);		tcp_mtu_probing(icsk, sk);

	dst_negative_advice(sk);		dst_negative_advice(sk);
			} else {
			sk_rethink_txhash(sk);
	}		}

	retry_until = net->ipv4.sysctl_tcp_retries2;		retry_until = net->ipv4.sysctl_tcp_retries2;