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Date: Wed, 23 Aug 2017 22:25:53 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Cong Wang <xiyou.wangcong@...il.com>
Cc: netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [Patch net-next] net_sched: kill u32_node pointer in Qdisc
Wed, Aug 23, 2017 at 07:58:54PM CEST, xiyou.wangcong@...il.com wrote:
>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.
Thanks for taking care of this. Comments below.
>
>Cc: Jamal Hadi Salim <jhs@...atatu.com>
>Cc: Jiri Pirko <jiri@...nulli.us>
>Signed-off-by: Cong Wang <xiyou.wangcong@...il.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;
Why not use rhashtable?
>+
>+#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);
This is over 80cols.
>+ 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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