[TCP]: Add pluggable congestion control algorithm infrastructure.

Allow TCP to have multiple pluggable congestion control algorithms.
Algorithms are defined by a set of operations and can be built in
or modules.  The legacy "new RENO" algorithm is used as a starting
point and fallback.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 195 insertions, 0 deletions

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
new file mode 100644
index 000000000000..665394a63ae4
--- /dev/null
+++ b/net/ipv4/tcp_cong.c
@@ -0,0 +1,195 @@
+/*
+ * Plugable TCP congestion control support and newReno
+ * congestion control.
+ * Based on ideas from I/O scheduler suport and Web100.
+ *
+ * Copyright (C) 2005 Stephen Hemminger <shemminger@osdl.org>
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/mm.h>
+#include <linux/types.h>
+#include <linux/list.h>
+#include <net/tcp.h>
+
+static DEFINE_SPINLOCK(tcp_cong_list_lock);
+static LIST_HEAD(tcp_cong_list);
+
+/* Simple linear search, don't expect many entries! */
+static struct tcp_congestion_ops *tcp_ca_find(const char *name)
+{
+        struct tcp_congestion_ops *e;
+
+        list_for_each_entry(e, &tcp_cong_list, list) {
+                if (strcmp(e->name, name) == 0)
+                        return e;
+        }
+
+        return NULL;
+}
+
+/*
+ * Attach new congestion control algorthim to the list
+ * of available options.
+ */
+int tcp_register_congestion_control(struct tcp_congestion_ops *ca)
+{
+        int ret = 0;
+
+        /* all algorithms must implement ssthresh and cong_avoid ops */
+        if (!ca->ssthresh || !ca->cong_avoid || !ca->min_cwnd) {
+                printk(KERN_ERR "TCP %s does not implement required ops\n",
+                       ca->name);
+                return -EINVAL;
+        }
+
+        spin_lock(&tcp_cong_list_lock);
+        if (tcp_ca_find(ca->name)) {
+                printk(KERN_NOTICE "TCP %s already registered\n", ca->name);
+                ret = -EEXIST;
+        } else {
+                list_add_rcu(&ca->list, &tcp_cong_list);
+                printk(KERN_INFO "TCP %s registered\n", ca->name);
+        }
+        spin_unlock(&tcp_cong_list_lock);
+
+        return ret;
+}
+EXPORT_SYMBOL_GPL(tcp_register_congestion_control);
+
+/*
+ * Remove congestion control algorithm, called from
+ * the module's remove function.  Module ref counts are used
+ * to ensure that this can't be done till all sockets using
+ * that method are closed.
+ */
+void tcp_unregister_congestion_control(struct tcp_congestion_ops *ca)
+{
+        spin_lock(&tcp_cong_list_lock);
+        list_del_rcu(&ca->list);
+        spin_unlock(&tcp_cong_list_lock);
+}
+EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control);
+
+/* Assign choice of congestion control. */
+void tcp_init_congestion_control(struct tcp_sock *tp)
+{
+        struct tcp_congestion_ops *ca;
+
+        rcu_read_lock();
+        list_for_each_entry_rcu(ca, &tcp_cong_list, list) {
+                if (try_module_get(ca->owner)) {
+                        tp->ca_ops = ca;
+                        break;
+                }
+
+        }
+        rcu_read_unlock();
+
+        if (tp->ca_ops->init)
+                tp->ca_ops->init(tp);
+}
+
+/* Manage refcounts on socket close. */
+void tcp_cleanup_congestion_control(struct tcp_sock *tp)
+{
+        if (tp->ca_ops->release)
+                tp->ca_ops->release(tp);
+        module_put(tp->ca_ops->owner);
+}
+
+/* Used by sysctl to change default congestion control */
+int tcp_set_default_congestion_control(const char *name)
+{
+        struct tcp_congestion_ops *ca;
+        int ret = -ENOENT;
+
+        spin_lock(&tcp_cong_list_lock);
+        ca = tcp_ca_find(name);
+#ifdef CONFIG_KMOD
+        if (!ca) {
+                spin_unlock(&tcp_cong_list_lock);
+
+                request_module("tcp_%s", name);
+                spin_lock(&tcp_cong_list_lock);
+                ca = tcp_ca_find(name);
+        }
+#endif
+
+        if (ca) {
+                list_move(&ca->list, &tcp_cong_list);
+                ret = 0;
+        }
+        spin_unlock(&tcp_cong_list_lock);
+
+        return ret;
+}
+
+/* Get current default congestion control */
+void tcp_get_default_congestion_control(char *name)
+{
+        struct tcp_congestion_ops *ca;
+        /* We will always have reno... */
+        BUG_ON(list_empty(&tcp_cong_list));
+
+        rcu_read_lock();
+        ca = list_entry(tcp_cong_list.next, struct tcp_congestion_ops, list);
+        strncpy(name, ca->name, TCP_CA_NAME_MAX);
+        rcu_read_unlock();
+}
+
+/*
+ * TCP Reno congestion control
+ * This is special case used for fallback as well.
+ */
+/* This is Jacobson's slow start and congestion avoidance.
+ * SIGCOMM '88, p. 328.
+ */
+void tcp_reno_cong_avoid(struct tcp_sock *tp, u32 ack, u32 rtt, u32 in_flight,
+                         int flag)
+{
+        if (in_flight < tp->snd_cwnd)
+                return;
+
+        if (tp->snd_cwnd <= tp->snd_ssthresh) {
+                /* In "safe" area, increase. */
+                if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+                        tp->snd_cwnd++;
+        } else {
+                /* In dangerous area, increase slowly.
+                 * In theory this is tp->snd_cwnd += 1 / tp->snd_cwnd
+                 */
+                if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+                        if (tp->snd_cwnd < tp->snd_cwnd_clamp)
+                                tp->snd_cwnd++;
+                        tp->snd_cwnd_cnt = 0;
+                } else
+                        tp->snd_cwnd_cnt++;
+        }
+}
+EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
+
+/* Slow start threshold is half the congestion window (min 2) */
+u32 tcp_reno_ssthresh(struct tcp_sock *tp)
+{
+        return max(tp->snd_cwnd >> 1U, 2U);
+}
+EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
+
+/* Lower bound on congestion window. */
+u32 tcp_reno_min_cwnd(struct tcp_sock *tp)
+{
+        return tp->snd_ssthresh/2;
+}
+EXPORT_SYMBOL_GPL(tcp_reno_min_cwnd);
+
+struct tcp_congestion_ops tcp_reno = {
+        .name           = "reno",
+        .owner          = THIS_MODULE,
+        .ssthresh       = tcp_reno_ssthresh,
+        .cong_avoid     = tcp_reno_cong_avoid,
+        .min_cwnd       = tcp_reno_min_cwnd,
+};
+
+EXPORT_SYMBOL_GPL(tcp_reno);