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-rw-r--r--Documentation/networking/ip-sysctl.txt12
-rw-r--r--include/linux/tcp.h4
-rw-r--r--include/net/tcp.h1
-rw-r--r--net/ipv4/sysctl_net_ipv4.c7
-rw-r--r--net/ipv4/tcp.c7
-rw-r--r--net/ipv4/tcp_input.c12
6 files changed, 42 insertions, 1 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index f147310d9af..2571a62d923 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -499,6 +499,18 @@ tcp_thin_linear_timeouts - BOOLEAN
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
+
UDP variables:
udp_mem - vector of 3 INTEGERs: min, pressure, max
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 3ba8b074612..a778ee02459 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -104,6 +104,7 @@ enum {
#define TCP_MD5SIG 14 /* TCP MD5 Signature (RFC2385) */
#define TCP_COOKIE_TRANSACTIONS 15 /* TCP Cookie Transactions */
#define TCP_THIN_LINEAR_TIMEOUTS 16 /* Use linear timeouts for thin streams*/
+#define TCP_THIN_DUPACK 17 /* Fast retrans. after 1 dupack */
/* for TCP_INFO socket option */
#define TCPI_OPT_TIMESTAMPS 1
@@ -343,7 +344,8 @@ struct tcp_sock {
u8 frto_counter; /* Number of new acks after RTO */
u8 nonagle : 4,/* Disable Nagle algorithm? */
thin_lto : 1,/* Use linear timeouts for thin streams */
- unused : 3;
+ thin_dupack : 1,/* Fast retransmit on first dupack */
+ unused : 2;
/* RTT measurement */
u32 srtt; /* smoothed round trip time << 3 */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 6278fc734ab..56f0aec40ed 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -245,6 +245,7 @@ extern int sysctl_tcp_slow_start_after_idle;
extern int sysctl_tcp_max_ssthresh;
extern int sysctl_tcp_cookie_size;
extern int sysctl_tcp_thin_linear_timeouts;
+extern int sysctl_tcp_thin_dupack;
extern atomic_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 e6a2460587d..c1bc074f61b 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -582,6 +582,13 @@ static struct ctl_table ipv4_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec
},
+ {
+ .procname = "tcp_thin_dupack",
+ .data = &sysctl_tcp_thin_dupack,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
{
.procname = "udp_mem",
.data = &sysctl_udp_mem,
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 21bae9afefe..5901010fad5 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2236,6 +2236,13 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
tp->thin_lto = val;
break;
+ case TCP_THIN_DUPACK:
+ if (val < 0 || val > 1)
+ err = -EINVAL;
+ else
+ tp->thin_dupack = val;
+ break;
+
case TCP_CORK:
/* When set indicates to always queue non-full frames.
* Later the user clears this option and we transmit
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 3fddc69cccc..788851ca8c5 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -89,6 +89,8 @@ int sysctl_tcp_frto __read_mostly = 2;
int sysctl_tcp_frto_response __read_mostly;
int sysctl_tcp_nometrics_save __read_mostly;
+int sysctl_tcp_thin_dupack __read_mostly;
+
int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
int sysctl_tcp_abc __read_mostly;
@@ -2447,6 +2449,16 @@ static int tcp_time_to_recover(struct sock *sk)
return 1;
}
+ /* 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 1;
+
return 0;
}