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) adds the option for the txhash to be changed before tcp_retries1
RTO retransmits. A new sysctl tcp_rto_txhash_prob represents the
probability that txhash will be changed. The default value is 0
which maintains previous behavior and a value of 100 will always
change it.
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.
v2: Added sysctl documentation and cleaned code
Tested with packetdrill tests
Signed-off-by: Lawrence Brakmo <bra...@fb.com>
---
Documentation/networking/ip-sysctl.txt | 11 +++++++++++
include/net/tcp.h | 1 +
net/ipv4/sysctl_net_ipv4.c | 10 ++++++++++
net/ipv4/tcp_input.c | 2 ++
net/ipv4/tcp_timer.c | 4 ++++
5 files changed, 28 insertions(+)
diff --git a/Documentation/networking/ip-sysctl.txt
b/Documentation/networking/ip-sysctl.txt
index 3db8c67..0e7f9ac 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -472,6 +472,17 @@ tcp_max_reordering - INTEGER
if paths are using per packet load balancing (like bonding rr mode)
Default: 300
+tcp_rto_txhash_prob - INTEGER
+ Probability [0 to 100] that we will recalculate txhash when a
+ packet is resent due to an RTO and the RTO for this packet has
+ fired less than tcp_retries1 times. It is always recalculated
+ after tcp_retries_times.
+
+ Setting it to 100 helps re-route around failed (or very congested
+ paths) as soon as possible. Otherwise application health checks may
+ fail and the connection may be terminated before the txhash has
+ a chance to change.
+
tcp_retrans_collapse - BOOLEAN
Bug-to-bug compatibility with some broken printers.
On retransmit try to send bigger packets to work around bugs in
diff --git a/include/net/tcp.h b/include/net/tcp.h
index f83b7f2..406d474 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -271,6 +271,7 @@ extern int sysctl_tcp_autocorking;
extern int sysctl_tcp_invalid_ratelimit;
extern int sysctl_tcp_pacing_ss_ratio;
extern int sysctl_tcp_pacing_ca_ratio;
+extern int sysctl_tcp_rto_txhash_prob;
extern atomic_long_t tcp_memory_allocated;
extern struct percpu_counter tcp_sockets_allocated;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 1cb67de..0b185a1 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -28,6 +28,7 @@
static int zero;
static int one = 1;
static int four = 4;
+static int hundred = 100;
static int thousand = 1000;
static int gso_max_segs = GSO_MAX_SEGS;
static int tcp_retr1_max = 255;
@@ -624,6 +625,15 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_dointvec_ms_jiffies,
},
{
+ .procname = "tcp_rto_txhash_prob",
+ .data = &sysctl_tcp_rto_txhash_prob,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &hundred,
+ },
+ {
.procname = "icmp_msgs_per_sec",
.data = &sysctl_icmp_msgs_per_sec,
.maxlen = sizeof(int),
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8c6ad2d..2fea29d 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -101,6 +101,8 @@ int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
int sysctl_tcp_early_retrans __read_mostly = 3;
int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
+int sysctl_tcp_rto_txhash_prob __read_mostly = 100;
+
#define FLAG_DATA 0x01 /* Incoming frame contained data.
*/
#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window
update. */
#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data.
*/
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index f712b41..8bdb215 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -192,6 +192,8 @@ static int tcp_write_timeout(struct sock *sk)
if (tp->syn_data && icsk->icsk_retransmits == 1)
NET_INC_STATS(sock_net(sk),
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;
syn_set = true;
@@ -213,6 +215,8 @@ static int tcp_write_timeout(struct sock *sk)
tcp_mtu_probing(icsk, sk);
dst_negative_advice(sk);
+ } else if (prandom_u32_max(100) < sysctl_tcp_rto_txhash_prob) {
+ sk_rethink_txhash(sk);
}
retry_until = net->ipv4.sysctl_tcp_retries2;
--
2.9.3
