tcp: remove low_latency sysctl

Was only checked by the removed prequeue code.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -353,12 +353,7 @@ tcp_l3mdev_accept - BOOLEAN
 	compiled with CONFIG_NET_L3_MASTER_DEV.
 
 tcp_low_latency - BOOLEAN
-	If set, the TCP stack makes decisions that prefer lower
-	latency as opposed to higher throughput.  By default, this
-	option is not set meaning that higher throughput is preferred.
-	An example of an application where this default should be
-	changed would be a Beowulf compute cluster.
-	Default: 0
+	This is a legacy option, it has no effect anymore.
 
 tcp_max_orphans - INTEGER
 	Maximal number of TCP sockets not attached to any user file handle,

include/net/tcp.h

@@ -256,7 +256,6 @@ extern int sysctl_tcp_rmem[3];
 extern int sysctl_tcp_app_win;
 extern int sysctl_tcp_adv_win_scale;
 extern int sysctl_tcp_frto;
-extern int sysctl_tcp_low_latency;
 extern int sysctl_tcp_nometrics_save;
 extern int sysctl_tcp_moderate_rcvbuf;
 extern int sysctl_tcp_tso_win_divisor;

net/ipv4/sysctl_net_ipv4.c

@@ -45,6 +45,9 @@ static int tcp_syn_retries_max = MAX_TCP_SYNCNT;
 static int ip_ping_group_range_min[] = { 0, 0 };
 static int ip_ping_group_range_max[] = { GID_T_MAX, GID_T_MAX };
 
+/* obsolete */
+static int sysctl_tcp_low_latency __read_mostly;
+
 /* Update system visible IP port range */
 static void set_local_port_range(struct net *net, int range[2])
 {

net/ipv4/tcp_ipv4.c

@@ -85,8 +85,6 @@
 #include <crypto/hash.h>
 #include <linux/scatterlist.h>
 
-int sysctl_tcp_low_latency __read_mostly;
-
 #ifdef CONFIG_TCP_MD5SIG
 static int tcp_v4_md5_hash_hdr(char *md5_hash, const struct tcp_md5sig_key *key,
 			       __be32 daddr, __be32 saddr, const struct tcphdr *th);