[PATCH] add sysctl to turn off caching metrics

[Stephen Hemminger <shemminger@xxxxxxxx>]

When running benchmarks and other experiments, it is often useful
not to save the route metrics (cwnd, rtt) from each connection.
Here is a simple way to do it with sysctl.  Not a new idea, it is part
of the web100 stuff as well.

Patch against 2.6.6-rc2

diff -Nru a/include/linux/sysctl.h b/include/linux/sysctl.h
--- a/include/linux/sysctl.h    Wed Apr 21 10:39:28 2004
+++ b/include/linux/sysctl.h    Wed Apr 21 10:39:28 2004
@@ -326,6 +326,7 @@
        NET_IPV4_IPFRAG_SECRET_INTERVAL=94,
        NET_TCP_WESTWOOD=95,
        NET_IPV4_IGMP_MAX_MSF=96,
+       NET_TCP_NO_METRICS_SAVE=97,
 };
 
 enum {
diff -Nru a/include/net/tcp.h b/include/net/tcp.h
--- a/include/net/tcp.h Wed Apr 21 10:39:28 2004
+++ b/include/net/tcp.h Wed Apr 21 10:39:28 2004
@@ -583,6 +583,7 @@
 extern int sysctl_tcp_frto;
 extern int sysctl_tcp_low_latency;
 extern int sysctl_tcp_westwood;
+extern int sysctl_tcp_nometrics_save;
 
 extern atomic_t tcp_memory_allocated;
 extern atomic_t tcp_sockets_allocated;
diff -Nru a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
--- a/net/ipv4/sysctl_net_ipv4.c        Wed Apr 21 10:39:28 2004
+++ b/net/ipv4/sysctl_net_ipv4.c        Wed Apr 21 10:39:28 2004
@@ -594,6 +594,14 @@
                .strategy       = &sysctl_jiffies
        },
        {
+               .ctl_name       = NET_TCP_NO_METRICS_SAVE,
+               .procname       = "tcp_no_metrics_save",
+               .data           = &sysctl_tcp_nometrics_save,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = &proc_dointvec,
+       },
+       {
                .ctl_name       = NET_TCP_WESTWOOD, 
                .procname       = "tcp_westwood",
                .data           = &sysctl_tcp_westwood,
@@ -601,6 +609,7 @@
                .mode           = 0644,
                .proc_handler   = &proc_dointvec,
        },
+
        { .ctl_name = 0 }
 };
 
diff -Nru a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
--- a/net/ipv4/tcp_input.c      Wed Apr 21 10:39:28 2004
+++ b/net/ipv4/tcp_input.c      Wed Apr 21 10:39:28 2004
@@ -87,6 +87,7 @@
 int sysctl_tcp_max_orphans = NR_FILE;
 int sysctl_tcp_frto;
 int sysctl_tcp_westwood;
+int sysctl_tcp_nometrics_save;
 
 #define FLAG_DATA              0x01 /* Incoming frame contained data.          
*/
 #define FLAG_WIN_UPDATE                0x02 /* Incoming ACK was a window 
update.       */
@@ -517,6 +518,9 @@
 {
        struct tcp_opt *tp = tcp_sk(sk);
        struct dst_entry *dst = __sk_dst_get(sk);
+
+       if (sysctl_tcp_nometrics_save)
+               return;
 
        dst_confirm(dst);