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Commit 2ee22a90 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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net_sched: act_mirred: remove spinlock in fast path 



Like act_gact, act_mirred can be lockless in packet processing

1) Use percpu stats
2) update lastuse only every clock tick to avoid false sharing
3) use rcu to protect tcfm_dev
4) Remove spinlock usage, as it is no longer needed.

Next step : add multi queue capability to ifb device

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Acked-by: default avatarJamal Hadi Salim <jhs@mojatatu.com>
Acked-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 56e5d1ca

include/net/tc_act/tc_mirred.h

+1 −1
Original line number Diff line number Diff line
@@ -8,7 +8,7 @@ struct tcf_mirred { 
	int			tcfm_eaction;

	int			tcfm_ifindex;

	int			tcfm_ok_push;

	struct net_device	*tcfm_dev;

	struct net_device __rcu	*tcfm_dev;

	struct list_head	tcfm_list;

};

#define to_mirred(a) \

net/sched/act_mirred.c

+30 −27
Original line number Diff line number Diff line
@@ -35,9 +35,11 @@ static LIST_HEAD(mirred_list); 
static void tcf_mirred_release(struct tc_action *a, int bind)

{

	struct tcf_mirred *m = to_mirred(a);

	struct net_device *dev = rcu_dereference_protected(m->tcfm_dev, 1);



	list_del(&m->tcfm_list);

	if (m->tcfm_dev)

		dev_put(m->tcfm_dev);

	if (dev)

		dev_put(dev);

}



static const struct nla_policy mirred_policy[TCA_MIRRED_MAX + 1] = {
@@ -94,7 +96,7 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla, 
		if (dev == NULL)

			return -EINVAL;

		ret = tcf_hash_create(parm->index, est, a, sizeof(*m),

				      bind, false);

				      bind, true);

		if (ret)

			return ret;

		ret = ACT_P_CREATED;
@@ -106,18 +108,18 @@ static int tcf_mirred_init(struct net *net, struct nlattr *nla, 
	}

	m = to_mirred(a);



	spin_lock_bh(&m->tcf_lock);

	ASSERT_RTNL();

	m->tcf_action = parm->action;

	m->tcfm_eaction = parm->eaction;

	if (dev != NULL) {

		m->tcfm_ifindex = parm->ifindex;

		if (ret != ACT_P_CREATED)

			dev_put(m->tcfm_dev);

			dev_put(rcu_dereference_protected(m->tcfm_dev, 1));

		dev_hold(dev);

		m->tcfm_dev = dev;

		rcu_assign_pointer(m->tcfm_dev, dev);

		m->tcfm_ok_push = ok_push;

	}

	spin_unlock_bh(&m->tcf_lock);



	if (ret == ACT_P_CREATED) {

		list_add(&m->tcfm_list, &mirred_list);

		tcf_hash_insert(a);
@@ -132,20 +134,22 @@ static int tcf_mirred(struct sk_buff *skb, const struct tc_action *a, 
	struct tcf_mirred *m = a->priv;

	struct net_device *dev;

	struct sk_buff *skb2;

	int retval, err;

	u32 at;

	int retval, err = 1;



	spin_lock(&m->tcf_lock);

	m->tcf_tm.lastuse = jiffies;

	bstats_update(&m->tcf_bstats, skb);

	tcf_lastuse_update(&m->tcf_tm);



	bstats_cpu_update(this_cpu_ptr(m->common.cpu_bstats), skb);



	dev = m->tcfm_dev;

	if (!dev) {

		printk_once(KERN_NOTICE "tc mirred: target device is gone\n");

	rcu_read_lock();

	retval = READ_ONCE(m->tcf_action);

	dev = rcu_dereference(m->tcfm_dev);

	if (unlikely(!dev)) {

		pr_notice_once("tc mirred: target device is gone\n");

		goto out;

	}



	if (!(dev->flags & IFF_UP)) {

	if (unlikely(!(dev->flags & IFF_UP))) {

		net_notice_ratelimited("tc mirred to Houston: device %s is down\n",

				       dev->name);

		goto out;
@@ -153,7 +157,7 @@ static int tcf_mirred(struct sk_buff *skb, const struct tc_action *a, 


	at = G_TC_AT(skb->tc_verd);

	skb2 = skb_clone(skb, GFP_ATOMIC);

	if (skb2 == NULL)

	if (!skb2)

		goto out;



	if (!(at & AT_EGRESS)) {
@@ -169,16 +173,13 @@ static int tcf_mirred(struct sk_buff *skb, const struct tc_action *a, 
	skb2->dev = dev;

	err = dev_queue_xmit(skb2);



out:

	if (err) {

		m->tcf_qstats.overlimits++;

out:

		qstats_overlimit_inc(this_cpu_ptr(m->common.cpu_qstats));

		if (m->tcfm_eaction != TCA_EGRESS_MIRROR)

			retval = TC_ACT_SHOT;

		else

			retval = m->tcf_action;

	} else

		retval = m->tcf_action;

	spin_unlock(&m->tcf_lock);

	}

	rcu_read_unlock();



	return retval;

}
@@ -217,14 +218,16 @@ static int mirred_device_event(struct notifier_block *unused, 
	struct net_device *dev = netdev_notifier_info_to_dev(ptr);

	struct tcf_mirred *m;



	ASSERT_RTNL();

	if (event == NETDEV_UNREGISTER)

		list_for_each_entry(m, &mirred_list, tcfm_list) {

			spin_lock_bh(&m->tcf_lock);

			if (m->tcfm_dev == dev) {

			if (rcu_access_pointer(m->tcfm_dev) == dev) {

				dev_put(dev);

				m->tcfm_dev = NULL;

				/* Note : no rcu grace period necessary, as

				 * net_device are already rcu protected.

				 */

				RCU_INIT_POINTER(m->tcfm_dev, NULL);

			}

			spin_unlock_bh(&m->tcf_lock);

		}



	return NOTIFY_DONE;