net_sched: add reverse binding for tc class

TC filters when used as classifiers are bound to TC classes.
However, there is a hidden difference when adding them in different
orders:

1. If we add tc classes before its filters, everything is fine.
   Logically, the classes exist before we specify their ID's in
   filters, it is easy to bind them together, just as in the current
   code base.

2. If we add tc filters before the tc classes they bind, we have to
   do dynamic lookup in fast path. What's worse, this happens all
   the time not just once, because on fast path tcf_result is passed
   on stack, there is no way to propagate back to the one in tc filters.

This hidden difference hurts performance silently if we have many tc
classes in hierarchy.

This patch intends to close this gap by doing the reverse binding when
we create a new class, in this case we can actually search all the
filters in its parent, match and fixup by classid. And because
tcf_result is specific to each type of tc filter, we have to introduce
a new ops for each filter to tell how to bind the class.

Note, we still can NOT totally get rid of those class lookup in
->enqueue() because cgroup and flow filters have no way to determine
the classid at setup time, they still have to go through dynamic lookup.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 66 insertions, 2 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index e7f8e4bfd4ec..929b024f41ba 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -35,6 +35,7 @@
 #include <net/sock.h>
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
+#include <net/pkt_cls.h>
 
 /*
 
@@ -1648,6 +1649,64 @@ static int tclass_del_notify(struct net *net,
                               n->nlmsg_flags & NLM_F_ECHO);
 }
 
+#ifdef CONFIG_NET_CLS
+
+struct tcf_bind_args {
+        struct tcf_walker w;
+        u32 classid;
+        unsigned long cl;
+};
+
+static int tcf_node_bind(struct tcf_proto *tp, void *n, struct tcf_walker *arg)
+{
+        struct tcf_bind_args *a = (void *)arg;
+
+        if (tp->ops->bind_class) {
+                tcf_tree_lock(tp);
+                tp->ops->bind_class(n, a->classid, a->cl);
+                tcf_tree_unlock(tp);
+        }
+        return 0;
+}
+
+static void tc_bind_tclass(struct Qdisc *q, u32 portid, u32 clid,
+                           unsigned long new_cl)
+{
+        const struct Qdisc_class_ops *cops = q->ops->cl_ops;
+        struct tcf_block *block;
+        struct tcf_chain *chain;
+        unsigned long cl;
+
+        cl = cops->find(q, portid);
+        if (!cl)
+                return;
+        block = cops->tcf_block(q, cl);
+        if (!block)
+                return;
+        list_for_each_entry(chain, &block->chain_list, list) {
+                struct tcf_proto *tp;
+
+                for (tp = rtnl_dereference(chain->filter_chain);
+                     tp; tp = rtnl_dereference(tp->next)) {
+                        struct tcf_bind_args arg = {};
+
+                        arg.w.fn = tcf_node_bind;
+                        arg.classid = clid;
+                        arg.cl = new_cl;
+                        tp->ops->walk(tp, &arg.w);
+                }
+        }
+}
+
+#else
+
+static void tc_bind_tclass(struct Qdisc *q, u32 portid, u32 clid,
+                           unsigned long new_cl)
+{
+}
+
+#endif
+
 static int tc_ctl_tclass(struct sk_buff *skb, struct nlmsghdr *n,
                          struct netlink_ext_ack *extack)
 {
@@ -1753,6 +1812,8 @@ static int tc_ctl_tclass(struct sk_buff *skb, struct nlmsghdr *n,
                         break;
                 case RTM_DELTCLASS:
                         err = tclass_del_notify(net, cops, skb, n, q, cl);
+                        /* Unbind the class with flilters with 0 */
+                        tc_bind_tclass(q, portid, clid, 0);
                         goto out;
                 case RTM_GETTCLASS:
                         err = tclass_notify(net, skb, n, q, cl, RTM_NEWTCLASS);
@@ -1767,9 +1828,12 @@ static int tc_ctl_tclass(struct sk_buff *skb, struct nlmsghdr *n,
         err = -EOPNOTSUPP;
         if (cops->change)
                 err = cops->change(q, clid, portid, tca, &new_cl);
-        if (err == 0)
+        if (err == 0) {
                 tclass_notify(net, skb, n, q, new_cl, RTM_NEWTCLASS);
-
+                /* We just create a new class, need to do reverse binding. */
+                if (cl != new_cl)
+                        tc_bind_tclass(q, portid, clid, new_cl);
+        }
 out:
         return err;
 }