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Date: Thu, 20 Jan 2011 14:48:19 +0100
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>, Patrick McHardy <kaber@...sh.net>,
Jesper Dangaard Brouer <hawk@...u.dk>,
Jarek Poplawski <jarkao2@...il.com>, jamal <hadi@...erus.ca>
Subject: [PATCH net-next-2.6] 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@...il.com>
CC: Patrick McHardy <kaber@...sh.net>
CC: Jesper Dangaard Brouer <hawk@...u.dk>
CC: Jarek Poplawski <jarkao2@...il.com>
CC: Jamal Hadi Salim <hadi@...erus.ca>
CC: Stephen Hemminger <shemminger@...tta.com>
---
include/net/sch_generic.h | 21 +++++++++++++++------
net/core/dev.c | 8 +++++---
net/sched/sch_api.c | 26 +++++++++++++++++---------
net/sched/sch_generic.c | 2 +-
4 files changed, 38 insertions(+), 19 deletions(-)
diff --git a/include/net/sch_generic.h b/include/net/sch_generic.h
index e9eee99..d67cc34 100644
--- a/include/net/sch_generic.h
+++ b/include/net/sch_generic.h
@@ -35,6 +35,7 @@ enum qdisc___state_t {
};
struct qdisc_size_table {
+ struct rcu_head rcu;
struct list_head list;
struct tc_sizespec szopts;
int refcnt;
@@ -53,7 +54,7 @@ struct Qdisc {
#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;
@@ -331,8 +332,8 @@ extern struct Qdisc *qdisc_alloc(struct netdev_queue *dev_queue,
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);
@@ -411,12 +412,20 @@ enum net_xmit_qdisc_t {
#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);
}
diff --git a/net/core/dev.c b/net/core/dev.c
index 8b1d886..f27882e 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2325,15 +2325,18 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
struct netdev_queue *txq)
{
spinlock_t *root_lock = qdisc_lock(q);
- bool contended = qdisc_is_running(q);
+ bool contended;
int rc;
+ qdisc_skb_cb(skb)->pkt_len = skb->len;
+ qdisc_calculate_pkt_len(skb, q);
/*
* Heuristic to force contended enqueues to serialize on a
* separate lock before trying to get qdisc main lock.
* This permits __QDISC_STATE_RUNNING owner to get the lock more often
* and dequeue packets faster.
*/
+ contended = qdisc_is_running(q);
if (unlikely(contended))
spin_lock(&q->busylock);
@@ -2351,7 +2354,6 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
if (!(dev->priv_flags & IFF_XMIT_DST_RELEASE))
skb_dst_force(skb);
- qdisc_skb_cb(skb)->pkt_len = skb->len;
qdisc_bstats_update(q, skb);
if (sch_direct_xmit(skb, q, dev, txq, root_lock)) {
@@ -2366,7 +2368,7 @@ static inline int __dev_xmit_skb(struct sk_buff *skb, struct Qdisc *q,
rc = NET_XMIT_SUCCESS;
} else {
skb_dst_force(skb);
- rc = qdisc_enqueue_root(skb, q);
+ rc = q->enqueue(skb, q) & NET_XMIT_MASK;
if (qdisc_run_begin(q)) {
if (unlikely(contended)) {
spin_unlock(&q->busylock);
diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 36ac0ec..7043fd9 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -398,6 +398,11 @@ static struct qdisc_size_table *qdisc_get_stab(struct nlattr *opt)
return stab;
}
+static void stab_kfree_rcu(struct rcu_head *head)
+{
+ kfree(container_of(head, struct qdisc_size_table, rcu));
+}
+
void qdisc_put_stab(struct qdisc_size_table *tab)
{
if (!tab)
@@ -407,7 +412,7 @@ void qdisc_put_stab(struct qdisc_size_table *tab)
if (--tab->refcnt == 0) {
list_del(&tab->list);
- kfree(tab);
+ call_rcu_bh(&tab->rcu, stab_kfree_rcu);
}
spin_unlock(&qdisc_stab_lock);
@@ -430,7 +435,7 @@ nla_put_failure:
return -1;
}
-void qdisc_calculate_pkt_len(struct sk_buff *skb, struct qdisc_size_table *stab)
+void __qdisc_calculate_pkt_len(struct sk_buff *skb, const struct qdisc_size_table *stab)
{
int pkt_len, slot;
@@ -456,7 +461,7 @@ out:
pkt_len = 1;
qdisc_skb_cb(skb)->pkt_len = pkt_len;
}
-EXPORT_SYMBOL(qdisc_calculate_pkt_len);
+EXPORT_SYMBOL(__qdisc_calculate_pkt_len);
void qdisc_warn_nonwc(char *txt, struct Qdisc *qdisc)
{
@@ -835,7 +840,7 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue,
err = PTR_ERR(stab);
goto err_out4;
}
- sch->stab = stab;
+ rcu_assign_pointer(sch->stab, stab);
}
if (tca[TCA_RATE]) {
spinlock_t *root_lock;
@@ -875,7 +880,7 @@ err_out4:
* Any broken qdiscs that would require a ops->reset() here?
* The qdisc was never in action so it shouldn't be necessary.
*/
- qdisc_put_stab(sch->stab);
+ qdisc_put_stab(rtnl_dereference(sch->stab));
if (ops->destroy)
ops->destroy(sch);
goto err_out3;
@@ -883,7 +888,7 @@ err_out4:
static int qdisc_change(struct Qdisc *sch, struct nlattr **tca)
{
- struct qdisc_size_table *stab = NULL;
+ struct qdisc_size_table *ostab, *stab = NULL;
int err = 0;
if (tca[TCA_OPTIONS]) {
@@ -900,8 +905,9 @@ static int qdisc_change(struct Qdisc *sch, struct nlattr **tca)
return PTR_ERR(stab);
}
- qdisc_put_stab(sch->stab);
- sch->stab = stab;
+ ostab = rtnl_dereference(sch->stab);
+ rcu_assign_pointer(sch->stab, stab);
+ qdisc_put_stab(ostab);
if (tca[TCA_RATE]) {
/* NB: ignores errors from replace_estimator
@@ -1180,6 +1186,7 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
struct nlmsghdr *nlh;
unsigned char *b = skb_tail_pointer(skb);
struct gnet_dump d;
+ struct qdisc_size_table *stab;
nlh = NLMSG_NEW(skb, pid, seq, event, sizeof(*tcm), flags);
tcm = NLMSG_DATA(nlh);
@@ -1195,7 +1202,8 @@ static int tc_fill_qdisc(struct sk_buff *skb, struct Qdisc *q, u32 clid,
goto nla_put_failure;
q->qstats.qlen = q->q.qlen;
- if (q->stab && qdisc_dump_stab(skb, q->stab) < 0)
+ stab = rtnl_dereference(q->stab);
+ if (stab && qdisc_dump_stab(skb, stab) < 0)
goto nla_put_failure;
if (gnet_stats_start_copy_compat(skb, TCA_STATS2, TCA_STATS, TCA_XSTATS,
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 2f1cb62..cc17e79 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -632,7 +632,7 @@ void qdisc_destroy(struct Qdisc *qdisc)
#ifdef CONFIG_NET_SCHED
qdisc_list_del(qdisc);
- qdisc_put_stab(qdisc->stab);
+ qdisc_put_stab(rtnl_dereference(qdisc->stab));
#endif
gen_kill_estimator(&qdisc->bstats, &qdisc->rate_est);
if (ops->reset)
--
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