[Patch net-next] net_sched: kill u32_node pointer in Qdisc

* [Patch net-next] net_sched: kill u32_node pointer in Qdisc
@ 2017-08-23 17:58 Cong Wang
  2017-08-23 20:25 ` Jiri Pirko
  0 siblings, 1 reply; 8+ messages in thread
From: Cong Wang @ 2017-08-23 17:58 UTC (permalink / raw)
  To: netdev; +Cc: Cong Wang, Jamal Hadi Salim, Jiri Pirko

It is ugly to hide a u32-filter-specific pointer inside Qdisc,
this breaks the TC layers:

1. Qdisc is a generic representation, should not have any specific
   data of any type

2. Qdisc layer is above filter layer, should only save filters in
   the list of struct tcf_proto.

This pointer is used as the head of the chain of u32 hash tables,
that is struct tc_u_hnode, because u32 filter is very special,
it allows to create multiple hash tables within one qdisc and
across multiple u32 filters.

Instead of using this ugly pointer, we can just save it in a global
hash table key'ed by (dev ifindex, qdisc handle), therefore we can
still treat it as a per qdisc basis data structure conceptually.

Of course, because of network namespaces, this key is not unique
at all, but it is fine as we already have a pointer to Qdisc in
struct tc_u_common, we can just compare the pointers when collision.

And this only affects slow paths, has no impact to fast path,
thanks to the pointer ->tp_c.

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
 include/net/sch_generic.h |  1 -
 net/sched/cls_u32.c       | 55 +++++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 51 insertions(+), 5 deletions(-)

diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index d817585aa5df..c30b634c5f82 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -75,7 +75,6 @@ struct Qdisc {
 	struct hlist_node       hash;
 	u32			handle;
 	u32			parent;
-	void			*u32_node;
 
 	struct netdev_queue	*dev_queue;
 
diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index af22742d2847..816d8622df02 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -40,6 +40,8 @@
 #include <linux/rtnetlink.h>
 #include <linux/skbuff.h>
 #include <linux/bitmap.h>
+#include <linux/netdevice.h>
+#include <linux/hash.h>
 #include <net/netlink.h>
 #include <net/act_api.h>
 #include <net/pkt_cls.h>
@@ -92,6 +94,7 @@ struct tc_u_common {
 	struct Qdisc		*q;
 	int			refcnt;
 	u32			hgenerator;
+	struct hlist_node	hnode;
 	struct rcu_head		rcu;
 };
 
@@ -323,12 +326,40 @@ static u32 gen_new_htid(struct tc_u_common *tp_c)
 	return i > 0 ? (tp_c->hgenerator|0x800)<<20 : 0;
 }
 
+static struct hlist_head *tc_u_common_hash;
+
+#define U32_HASH_SHIFT 10
+#define U32_HASH_SIZE (1 << U32_HASH_SHIFT)
+
+static unsigned int tc_u_hash(const struct tcf_proto *tp)
+{
+	struct net_device *dev = tp->q->dev_queue->dev;
+	u32 qhandle = tp->q->handle;
+	int ifindex = dev->ifindex;
+
+	return hash_64((u64)ifindex << 32 | qhandle, U32_HASH_SHIFT);
+}
+
+static struct tc_u_common *tc_u_common_find(const struct tcf_proto *tp)
+{
+	struct tc_u_common *tc;
+	unsigned int h;
+
+	h = tc_u_hash(tp);
+	hlist_for_each_entry(tc, &tc_u_common_hash[h], hnode) {
+		if (tc->q == tp->q)
+			return tc;
+	}
+	return NULL;
+}
+
 static int u32_init(struct tcf_proto *tp)
 {
 	struct tc_u_hnode *root_ht;
 	struct tc_u_common *tp_c;
+	unsigned int h;
 
-	tp_c = tp->q->u32_node;
+	tp_c = tc_u_common_find(tp);
 
 	root_ht = kzalloc(sizeof(*root_ht), GFP_KERNEL);
 	if (root_ht == NULL)
@@ -345,7 +376,10 @@ static int u32_init(struct tcf_proto *tp)
 			return -ENOBUFS;
 		}
 		tp_c->q = tp->q;
-		tp->q->u32_node = tp_c;
+		INIT_HLIST_NODE(&tp_c->hnode);
+
+		h = tc_u_hash(tp);
+		hlist_add_head(&tp_c->hnode, &tc_u_common_hash[h]);
 	}
 
 	tp_c->refcnt++;
@@ -585,7 +619,7 @@ static void u32_destroy(struct tcf_proto *tp)
 	if (--tp_c->refcnt == 0) {
 		struct tc_u_hnode *ht;
 
-		tp->q->u32_node = NULL;
+		hlist_del(&tp_c->hnode);
 
 		for (ht = rtnl_dereference(tp_c->hlist);
 		     ht;
@@ -1213,6 +1247,8 @@ static struct tcf_proto_ops cls_u32_ops __read_mostly = {
 
 static int __init init_u32(void)
 {
+	int i, ret;
+
 	pr_info("u32 classifier\n");
 #ifdef CONFIG_CLS_U32_PERF
 	pr_info("    Performance counters on\n");
@@ -1223,12 +1259,23 @@ static int __init init_u32(void)
 #ifdef CONFIG_NET_CLS_ACT
 	pr_info("    Actions configured\n");
 #endif
-	return register_tcf_proto_ops(&cls_u32_ops);
+	tc_u_common_hash = kvmalloc_array(U32_HASH_SIZE, sizeof(struct hlist_head), GFP_KERNEL);
+	if (!tc_u_common_hash)
+		return -ENOMEM;
+
+	for (i = 0; i < U32_HASH_SIZE; i++)
+		INIT_HLIST_HEAD(&tc_u_common_hash[i]);
+
+	ret = register_tcf_proto_ops(&cls_u32_ops);
+	if (ret)
+		kvfree(tc_u_common_hash);
+	return ret;
 }
 
 static void __exit exit_u32(void)
 {
 	unregister_tcf_proto_ops(&cls_u32_ops);
+	kvfree(tc_u_common_hash);
 }
 
 module_init(init_u32)
-- 
2.13.0

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