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Commit a2da570d authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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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: default avatarEric 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: default avatarDavid S. Miller <davem@davemloft.net>
parent fd245a4a

include/net/sch_generic.h

+15 −6
Original line number Diff line number Diff line
@@ -36,6 +36,7 @@ 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;
@@ -349,8 +350,8 @@ 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);
@@ -429,12 +430,20 @@ 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);

}

net/core/dev.c

+5 −3
Original line number Diff line number Diff line
@@ -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);

net/sched/sch_api.c

+17 −9
Original line number Diff line number Diff line
@@ -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 @@ static int qdisc_dump_stab(struct sk_buff *skb, struct qdisc_size_table *stab) 
	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 @@ void qdisc_calculate_pkt_len(struct sk_buff *skb, struct qdisc_size_table *stab) 
		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 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue, 
	 * 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 @@ qdisc_create(struct net_device *dev, struct netdev_queue *dev_queue, 


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,

net/sched/sch_generic.c

+1 −1
Original line number Diff line number Diff line
@@ -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)