net_sched: RCU conversion of stab
This patch converts stab qdisc management to RCU, so that we can perform
the qdisc_calculate_pkt_len() call before getting qdisc lock.
This shortens the lock's held time in __dev_xmit_skb().
This permits more qdiscs to get TCQ_F_CAN_BYPASS status, avoiding lot of
cache misses and so reducing latencies.
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
CC: Patrick McHardy <kaber@trash.net>
CC: Jesper Dangaard Brouer <hawk@diku.dk>
CC: Jarek Poplawski <jarkao2@gmail.com>
CC: Jamal Hadi Salim <hadi@cyberus.ca>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index f6345f5..d531baa 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -36,6 +36,7 @@
};
struct qdisc_size_table {
+ struct rcu_head rcu;
struct list_head list;
struct tc_sizespec szopts;
int refcnt;
@@ -53,7 +54,7 @@
#define TCQ_F_WARN_NONWC (1 << 16)
int padded;
struct Qdisc_ops *ops;
- struct qdisc_size_table *stab;
+ struct qdisc_size_table __rcu *stab;
struct list_head list;
u32 handle;
u32 parent;
@@ -349,8 +350,8 @@
struct Qdisc_ops *ops);
extern struct Qdisc *qdisc_create_dflt(struct netdev_queue *dev_queue,
struct Qdisc_ops *ops, u32 parentid);
-extern void qdisc_calculate_pkt_len(struct sk_buff *skb,
- struct qdisc_size_table *stab);
+extern void __qdisc_calculate_pkt_len(struct sk_buff *skb,
+ const struct qdisc_size_table *stab);
extern void tcf_destroy(struct tcf_proto *tp);
extern void tcf_destroy_chain(struct tcf_proto **fl);
@@ -429,12 +430,20 @@
#define net_xmit_drop_count(e) (1)
#endif
-static inline int qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch)
+static inline void qdisc_calculate_pkt_len(struct sk_buff *skb,
+ const struct Qdisc *sch)
{
#ifdef CONFIG_NET_SCHED
- if (sch->stab)
- qdisc_calculate_pkt_len(skb, sch->stab);
+ struct qdisc_size_table *stab = rcu_dereference_bh(sch->stab);
+
+ if (stab)
+ __qdisc_calculate_pkt_len(skb, stab);
#endif
+}
+
+static inline int qdisc_enqueue(struct sk_buff *skb, struct Qdisc *sch)
+{
+ qdisc_calculate_pkt_len(skb, sch);
return sch->enqueue(skb, sch);
}