tcp: Added knobs to tune initial window sizes

gistfile1.diff

commit e4d08801d7cfb46a2f8cd46049c455f63d85a064
Author: Alexey Ivanov <rbtz@yandex-team.ru>
Date:   Wed Jul 18 22:14:36 2012 +0400

    YANDEX: tcp: Added knobs to tune initial window sizes
    
    Added following sysctls
    
    /* TCP initial congestion window */
    TCP_INIT_CWND -> net.ipv4.tcp_init_cwnd
    
    /* Offer an initial receive window of 10 mss. */
    TCP_DEFAULT_INIT_RCVWND -> net.ipv4.tcp_init_rcvwnd

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 60b7480..05f7607 100644
 extern struct percpu_counter tcp_sockets_allocated;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index ea5acfb..b2d5c94 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -25,6 +25,7 @@
 #include <net/ping.h>
 
 static int zero;
+static int one = 1;
 static int tcp_retr1_max = 255;
 static int ip_local_port_range_min[] = { 1, 1 };
 static int ip_local_port_range_max[] = { 65535, 65535 };
@@ -688,6 +689,22 @@ static struct ctl_table ipv4_table[] = {
                .proc_handler   = proc_dointvec_ms_jiffies,
        },
        {
+               .procname       = "tcp_init_cwnd",
+               .data           = &sysctl_tcp_init_cwnd,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = &one
+       },
+       {
+               .procname       = "tcp_init_rcvwnd",
+               .data           = &sysctl_tcp_init_rcvwnd,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = &one
+       },
+       {
                .procname       = "udp_mem",
                .data           = &sysctl_udp_mem,
                .maxlen         = sizeof(sysctl_udp_mem),
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index d2fa705..388ca95 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -86,6 +86,10 @@ int sysctl_tcp_app_win __read_mostly = 31;
 int sysctl_tcp_adv_win_scale __read_mostly = 1;
 EXPORT_SYMBOL(sysctl_tcp_adv_win_scale);
 
+/* TCP initial congestion window as per draft-hkchu-tcpm-initcwnd-01 */
+int sysctl_tcp_init_cwnd __read_mostly = 10; /* TCP_INIT_CWND */
+EXPORT_SYMBOL(sysctl_tcp_init_cwnd);
+
 int sysctl_tcp_stdurg __read_mostly;
 int sysctl_tcp_rfc1337 __read_mostly;
 int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
@@ -267,7 +271,7 @@ static void tcp_fixup_sndbuf(struct sock *sk)
 {
        int sndmem = SKB_TRUESIZE(tcp_sk(sk)->rx_opt.mss_clamp + MAX_TCP_HEADER);
 
-       sndmem *= TCP_INIT_CWND;
+       sndmem *= sysctl_tcp_init_cwnd;
        if (sk->sk_sndbuf < sndmem)
                sk->sk_sndbuf = min(sndmem, sysctl_tcp_wmem[2]);
 }
@@ -347,14 +351,14 @@ static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
 static void tcp_fixup_rcvbuf(struct sock *sk)
 {
        u32 mss = tcp_sk(sk)->advmss;
-       u32 icwnd = TCP_DEFAULT_INIT_RCVWND;
+       u32 icwnd = sysctl_tcp_init_rcvwnd;
        int rcvmem;
 
        /* Limit to 10 segments if mss <= 1460,
         * or 14600/mss segments, with a minimum of two segments.
         */
        if (mss > 1460)
-               icwnd = max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
+               icwnd = max_t(u32, (1460 * sysctl_tcp_init_rcvwnd) / mss, 2);
 
        rcvmem = SKB_TRUESIZE(mss + MAX_TCP_HEADER);
        while (tcp_win_from_space(rcvmem) < mss)
@@ -833,7 +837,7 @@ __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
        __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
 
        if (!cwnd)
-               cwnd = TCP_INIT_CWND;
+               cwnd = sysctl_tcp_init_cwnd;
        return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
 }
 
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index af66ca9..4be5dea 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1885,7 +1885,7 @@ static int tcp_v4_init_sock(struct sock *sk)
         * algorithms that we must have the following bandaid to talk
         * efficiently to them.  -DaveM
         */
-       tp->snd_cwnd = TCP_INIT_CWND;
+       tp->snd_cwnd = sysctl_tcp_init_cwnd;
 
        /* See draft-stevens-tcpca-spec-01 for discussion of the
         * initialization of these values.
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 63b9c69..5228478 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -488,7 +488,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
                 * algorithms that we must have the following bandaid to talk
                 * efficiently to them.  -DaveM
                 */
-               newtp->snd_cwnd = TCP_INIT_CWND;
+               newtp->snd_cwnd = sysctl_tcp_init_cwnd;
                newtp->snd_cwnd_cnt = 0;
                newtp->bytes_acked = 0;
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 524b585..340cbc8 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -63,6 +63,9 @@ int sysctl_tcp_slow_start_after_idle __read_mostly = 1;
 int sysctl_tcp_cookie_size __read_mostly = 0; /* TCP_COOKIE_MAX */
 EXPORT_SYMBOL_GPL(sysctl_tcp_cookie_size);
 
+/* Offer an initial receive window of 10 mss. */
+int sysctl_tcp_init_rcvwnd __read_mostly = 10; /* TCP_DEFAULT_INIT_RCVWND */
+EXPORT_SYMBOL_GPL(sysctl_tcp_init_rcvwnd);
 
 /* Account for new data that has been sent to the network. */
 static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
@@ -229,14 +232,14 @@ void tcp_select_initial_window(int __space, __u32 mss,
        }
 
        /* Set initial window to a value enough for senders starting with
-        * initial congestion window of TCP_DEFAULT_INIT_RCVWND. Place
+        * initial congestion window of sysctl_tcp_init_rcvwnd. Place
         * a limit on the initial window when mss is larger than 1460.
         */
        if (mss > (1 << *rcv_wscale)) {
-               int init_cwnd = TCP_DEFAULT_INIT_RCVWND;
+               int init_cwnd = sysctl_tcp_init_rcvwnd;
                if (mss > 1460)
                        init_cwnd =
-                       max_t(u32, (1460 * TCP_DEFAULT_INIT_RCVWND) / mss, 2);
+                       max_t(u32, (1460 * sysctl_tcp_init_rcvwnd) / mss, 2);
                /* when initializing use the value from init_rcv_wnd
                 * rather than the default from above
                 */