tcp: remove thin_dupack feature
Thin stream DUPACK is to start fast recovery on only one DUPACK
provided the connection is a thin stream (i.e., low inflight). But
this older feature is now subsumed with RACK. If a connection
receives only a single DUPACK, RACK would arm a reordering timer
and soon starts fast recovery instead of timeout if no further
ACKs are received.
The socket option (THIN_DUPACK) is kept as a nop for compatibility.
Note that this patch does not change another thin-stream feature
which enables linear RTO. Although it might be good to generalize
that in the future (i.e., linear RTO for the first say 3 retries).
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 7de2cf7..aa1bb49 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -703,18 +703,6 @@
Documentation/networking/tcp-thin.txt
Default: 0
-tcp_thin_dupack - BOOLEAN
- Enable dynamic triggering of retransmissions after one dupACK
- for thin streams. If set, a check is performed upon reception
- of a dupACK to determine if the stream is thin (less than 4
- packets in flight). As long as the stream is found to be thin,
- data is retransmitted on the first received dupACK. This
- improves retransmission latency for non-aggressive thin
- streams, often found to be time-dependent.
- For more information on thin streams, see
- Documentation/networking/tcp-thin.txt
- Default: 0
-
tcp_limit_output_bytes - INTEGER
Controls TCP Small Queue limit per tcp socket.
TCP bulk sender tends to increase packets in flight until it
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 4733368..6c22332 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -220,7 +220,7 @@ struct tcp_sock {
unused:5;
u8 nonagle : 4,/* Disable Nagle algorithm? */
thin_lto : 1,/* Use linear timeouts for thin streams */
- thin_dupack : 1,/* Fast retransmit on first dupack */
+ unused1 : 1,
repair : 1,
frto : 1;/* F-RTO (RFC5682) activated in CA_Loss */
u8 repair_queue;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 0f2d37e..c8d2836 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -537,13 +537,6 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_dointvec
},
{
- .procname = "tcp_thin_dupack",
- .data = &sysctl_tcp_thin_dupack,
- .maxlen = sizeof(int),
- .mode = 0644,
- .proc_handler = proc_dointvec
- },
- {
.procname = "tcp_early_retrans",
.data = &sysctl_tcp_early_retrans,
.maxlen = sizeof(int),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index d9023e8..aba6ea7 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2474,9 +2474,6 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
case TCP_THIN_DUPACK:
if (val < 0 || val > 1)
err = -EINVAL;
- else {
- tp->thin_dupack = val;
- }
break;
case TCP_REPAIR:
@@ -2966,8 +2963,9 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
case TCP_THIN_LINEAR_TIMEOUTS:
val = tp->thin_lto;
break;
+
case TCP_THIN_DUPACK:
- val = tp->thin_dupack;
+ val = 0;
break;
case TCP_REPAIR:
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 87315ab..39ebc20c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -95,9 +95,6 @@ int sysctl_tcp_rfc1337 __read_mostly;
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
int sysctl_tcp_frto __read_mostly = 2;
int sysctl_tcp_min_rtt_wlen __read_mostly = 300;
-
-int sysctl_tcp_thin_dupack __read_mostly;
-
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;
@@ -2170,16 +2167,6 @@ static bool tcp_time_to_recover(struct sock *sk, int flag)
if (tcp_dupack_heuristics(tp) > tp->reordering)
return true;
- /* If a thin stream is detected, retransmit after first
- * received dupack. Employ only if SACK is supported in order
- * to avoid possible corner-case series of spurious retransmissions
- * Use only if there are no unsent data.
- */
- if ((tp->thin_dupack || sysctl_tcp_thin_dupack) &&
- tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
- tcp_is_sack(tp) && !tcp_send_head(sk))
- return true;
-
return false;
}