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, 9 insertions, 0 deletions

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index 99ea4c74dd5b..10b8d851fc6b 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -1112,6 +1112,14 @@ static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg)
 	}
 }
 
+static void u32_bind_class(void *fh, u32 classid, unsigned long cl)
+{
+	struct tc_u_knode *n = fh;
+
+	if (n && n->res.classid == classid)
+		n->res.class = cl;
+}
+
 static int u32_dump(struct net *net, struct tcf_proto *tp, void *fh,
 		    struct sk_buff *skb, struct tcmsg *t)
 {
@@ -1242,6 +1250,7 @@ static struct tcf_proto_ops cls_u32_ops __read_mostly = {
 	.delete		=	u32_delete,
 	.walk		=	u32_walk,
 	.dump		=	u32_dump,
+	.bind_class	=	u32_bind_class,
 	.owner		=	THIS_MODULE,
 };