net: TCP thin linear timeouts

This patch will make TCP use only linear timeouts if the
stream is thin. This will help to avoid the very high latencies
that thin stream suffer because of exponential backoff. This
mechanism is only active if enabled by iocontrol or syscontrol
and the stream is identified as thin. A maximum of 6 linear
timeouts is tried before exponential backoff is resumed.

Signed-off-by: Andreas Petlund <apetlund@simula.no>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 8 insertions, 1 deletions

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;