[TCP]: Add two new spurious RTO responses to FRTO
New sysctl tcp_frto_response is added to select amongst these
responses:
- Rate halving based; reuses CA_CWR state (default)
- Very conservative; used to be the only one available (=1)
- Undo cwr; undoes ssthresh and cwnd reductions (=2)
The response with rate halving requires a new parameter to
tcp_enter_cwr because FRTO has already reduced ssthresh and
doing a second reduction there has to be prevented. In addition,
to keep things nice on 80 cols screen, a local variable was
added.
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 98e0fd2..c9ccb55 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -439,6 +439,7 @@
NET_TCP_AVAIL_CONG_CONTROL=122,
NET_TCP_ALLOWED_CONG_CONTROL=123,
NET_TCP_MAX_SSTHRESH=124,
+ NET_TCP_FRTO_RESPONSE=125,
};
enum {
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6d09f50..f0c9e34 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -220,6 +220,7 @@
extern int sysctl_tcp_adv_win_scale;
extern int sysctl_tcp_tw_reuse;
extern int sysctl_tcp_frto;
+extern int sysctl_tcp_frto_response;
extern int sysctl_tcp_low_latency;
extern int sysctl_tcp_dma_copybreak;
extern int sysctl_tcp_nometrics_save;
@@ -738,7 +739,7 @@
tp->left_out = tp->sacked_out + tp->lost_out;
}
-extern void tcp_enter_cwr(struct sock *sk);
+extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
extern __u32 tcp_init_cwnd(struct tcp_sock *tp, struct dst_entry *dst);
/* Slow start with delack produces 3 packets of burst, so that
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index d68effe..6817d64 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -647,6 +647,14 @@
.proc_handler = &proc_dointvec
},
{
+ .ctl_name = NET_TCP_FRTO_RESPONSE,
+ .procname = "tcp_frto_response",
+ .data = &sysctl_tcp_frto_response,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec
+ },
+ {
.ctl_name = NET_TCP_LOW_LATENCY,
.procname = "tcp_low_latency",
.data = &sysctl_tcp_low_latency,
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f6ba07f..322e43c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -86,6 +86,7 @@
int sysctl_tcp_rfc1337 __read_mostly;
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
int sysctl_tcp_frto __read_mostly;
+int sysctl_tcp_frto_response __read_mostly;
int sysctl_tcp_nometrics_save __read_mostly;
int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
@@ -762,15 +763,17 @@
}
/* Set slow start threshold and cwnd not falling to slow start */
-void tcp_enter_cwr(struct sock *sk)
+void tcp_enter_cwr(struct sock *sk, const int set_ssthresh)
{
struct tcp_sock *tp = tcp_sk(sk);
+ const struct inet_connection_sock *icsk = inet_csk(sk);
tp->prior_ssthresh = 0;
tp->bytes_acked = 0;
if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
tp->undo_marker = 0;
- tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
+ if (set_ssthresh)
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
tp->snd_cwnd = min(tp->snd_cwnd,
tcp_packets_in_flight(tp) + 1U);
tp->snd_cwnd_cnt = 0;
@@ -2003,7 +2006,7 @@
tp->retrans_stamp = 0;
if (flag&FLAG_ECE)
- tcp_enter_cwr(sk);
+ tcp_enter_cwr(sk, 1);
if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
int state = TCP_CA_Open;
@@ -2579,6 +2582,21 @@
tcp_moderate_cwnd(tp);
}
+/* A conservative spurious RTO response algorithm: reduce cwnd using
+ * rate halving and continue in congestion avoidance.
+ */
+static void tcp_ratehalving_spur_to_response(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ tcp_enter_cwr(sk, 0);
+ tp->high_seq = tp->frto_highmark; /* Smoother w/o this? - ij */
+}
+
+static void tcp_undo_spur_to_response(struct sock *sk)
+{
+ tcp_undo_cwr(sk, 1);
+}
+
/* F-RTO spurious RTO detection algorithm (RFC4138)
*
* F-RTO affects during two new ACKs following RTO (well, almost, see inline
@@ -2661,7 +2679,17 @@
tp->frto_counter = 2;
return 1;
} else /* frto_counter == 2 */ {
- tcp_conservative_spur_to_response(tp);
+ switch (sysctl_tcp_frto_response) {
+ case 2:
+ tcp_undo_spur_to_response(sk);
+ break;
+ case 1:
+ tcp_conservative_spur_to_response(tp);
+ break;
+ default:
+ tcp_ratehalving_spur_to_response(sk);
+ break;
+ };
tp->frto_counter = 0;
}
return 0;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 3c24881..d19b2f3 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -545,7 +545,7 @@
if (likely(err <= 0))
return err;
- tcp_enter_cwr(sk);
+ tcp_enter_cwr(sk, 1);
return net_xmit_eval(err);