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Subject[net-next PATCH v3 3/3] net: TCP thin dupack
Major changes:
-Possible to disable mechanisms by socket option
-Socket option value boundary check


Signed-off-by: Andreas Petlund <apetlund@simula.no>
---
include/linux/sysctl.h | 1 +
include/linux/tcp.h | 4 +++-
include/net/tcp.h | 1 +
net/ipv4/sysctl_net_ipv4.c | 7 +++++++
net/ipv4/tcp.c | 7 +++++++
net/ipv4/tcp_input.c | 11 +++++++++++
6 files changed, 30 insertions(+), 1 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index d840d75..ded3f20 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -426,6 +426,7 @@ enum
NET_TCP_MAX_SSTHRESH=124,
NET_TCP_FRTO_RESPONSE=125,
NET_TCP_FORCE_THIN_LINEAR_TIMEOUTS=126,
+ NET_TCP_FORCE_THIN_LINEAR_DUPACK=127,
};

enum {
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 67da706..c30ed17 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_LT 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; /* Disable Nagle algorithm? */
u8 thin_lt : 1,/* Use linear timeouts for thin streams */
- thin_undef : 7;
+ thin_dupack : 1,/* Fast retransmit on first dupack */
+ thin_undef : 6;

/* RTT measurement */
u32 srtt; /* smoothed round trip time << 3 */
diff --git a/include/net/tcp.h b/include/net/tcp.h
index bc5856a..af1253c 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_force_thin_linear_timeouts;
+extern int sysctl_tcp_force_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 cb2ed35..b097a58 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_force_thin_dupack",
+ .data = &sysctl_tcp_force_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 ce9aeb0..6d7cb9c 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_lt = 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 28e0296..c5a73ab 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_force_thin_dupack __read_mostly;
+
int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
int sysctl_tcp_abc __read_mostly;

@@ -2447,6 +2449,15 @@ 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_force_thin_dupack) &&
+ tcp_stream_is_thin(tp) && tcp_dupack_heuristics(tp) > 1 &&
+ tcp_is_sack(tp) && sk->sk_send_head == NULL)
+ return 1;
+
return 0;
}

--
1.6.3.3


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