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-rw-r--r--Documentation/networking/ip-sysctl.txt12
-rw-r--r--include/linux/tcp.h5
-rw-r--r--include/net/tcp.h4
-rw-r--r--net/ipv4/sysctl_net_ipv4.c7
-rw-r--r--net/ipv4/tcp.c7
-rw-r--r--net/ipv4/tcp_timer.c21
6 files changed, 54 insertions, 2 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 2dc7a1d97686..f147310d9af4 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -487,6 +487,18 @@ tcp_dma_copybreak - INTEGER
and CONFIG_NET_DMA is enabled.
Default: 4096
+tcp_thin_linear_timeouts - BOOLEAN
+ Enable dynamic triggering of linear timeouts for thin streams.
+ If set, a check is performed upon retransmission by timeout to
+ determine if the stream is thin (less than 4 packets in flight).
+ As long as the stream is found to be thin, up to 6 linear
+ timeouts may be performed before exponential backoff mode is
+ initiated. 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 7fee8a4df931..3ba8b074612f 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -103,6 +103,7 @@ enum {
#define TCP_CONGESTION 13 /* Congestion control algorithm */
#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*/
/* for TCP_INFO socket option */
#define TCPI_OPT_TIMESTAMPS 1
@@ -340,7 +341,9 @@ struct tcp_sock {
u32 frto_highmark; /* snd_nxt when RTO occurred */
u16 advmss; /* Advertised MSS */
u8 frto_counter; /* Number of new acks after RTO */
- u8 nonagle; /* Disable Nagle algorithm? */
+ u8 nonagle : 4,/* Disable Nagle algorithm? */
+ thin_lto : 1,/* Use linear timeouts for thin streams */
+ unused : 3;
/* RTT measurement */
u32 srtt; /* smoothed round trip time << 3 */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 0bdc3f640247..6278fc734abd 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -196,6 +196,9 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
#define TCP_NAGLE_CORK 2 /* Socket is corked */
#define TCP_NAGLE_PUSH 4 /* Cork is overridden for already queued data */
+/* TCP thin-stream limits */
+#define TCP_THIN_LINEAR_RETRIES 6 /* After 6 linear retries, do exp. backoff */
+
extern struct inet_timewait_death_row tcp_death_row;
/* sysctl variables for tcp */
@@ -241,6 +244,7 @@ extern int sysctl_tcp_workaround_signed_windows;
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 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 7e3712ce3994..e6a2460587d4 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -576,6 +576,13 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_dointvec
},
{
+ .procname = "tcp_thin_linear_timeouts",
+ .data = &sysctl_tcp_thin_linear_timeouts,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec
+ },
+ {
.procname = "udp_mem",
.data = &sysctl_udp_mem,
.maxlen = sizeof(sysctl_udp_mem),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index e471d037fcc9..21bae9afefea 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2229,6 +2229,13 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
}
break;
+ case TCP_THIN_LINEAR_TIMEOUTS:
+ if (val < 0 || val > 1)
+ err = -EINVAL;
+ else
+ tp->thin_lto = 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_timer.c b/net/ipv4/tcp_timer.c
index de7d1bf9114f..a17629b8912e 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -29,6 +29,7 @@ int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
int sysctl_tcp_orphan_retries __read_mostly;
+int sysctl_tcp_thin_linear_timeouts __read_mostly;
static void tcp_write_timer(unsigned long);
static void tcp_delack_timer(unsigned long);
@@ -415,7 +416,25 @@ void tcp_retransmit_timer(struct sock *sk)
icsk->icsk_retransmits++;
out_reset_timer:
- icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
+ /* If stream is thin, use linear timeouts. Since 'icsk_backoff' is
+ * used to reset timer, set to 0. Recalculate 'icsk_rto' as this
+ * might be increased if the stream oscillates between thin and thick,
+ * thus the old value might already be too high compared to the value
+ * set by 'tcp_set_rto' in tcp_input.c which resets the rto without
+ * backoff. Limit to TCP_THIN_LINEAR_RETRIES before initiating
+ * exponential backoff behaviour to avoid continue hammering
+ * linear-timeout retransmissions into a black hole
+ */
+ if (sk->sk_state == TCP_ESTABLISHED &&
+ (tp->thin_lto || sysctl_tcp_thin_linear_timeouts) &&
+ tcp_stream_is_thin(tp) &&
+ icsk->icsk_retransmits <= TCP_THIN_LINEAR_RETRIES) {
+ icsk->icsk_backoff = 0;
+ icsk->icsk_rto = min(__tcp_set_rto(tp), TCP_RTO_MAX);
+ } else {
+ /* Use normal (exponential) backoff */
+ icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
+ }
inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
if (retransmits_timed_out(sk, sysctl_tcp_retries1 + 1))
__sk_dst_reset(sk);