[PATCH net-next 4/4] act_mirred: use ACT_MIRRED when possible

[Paolo Abeni]

When mirred is invoked from the ingress path, and it wants to redirect
the processed packet, it can now use the ACT_MIRRED action,
filling the tcf_result accordingly, and avoiding a per packet
skb_clone().

Overall this gives a ~10% improvement in forwarding performance for the
TC S/W data path and TC S/W performances are now comparable to the
kernel openswitch datapath.

v1 -> v2: use ACT_MIRRED instead of ACT_REDIRECT

Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 net/sched/act_mirred.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index eeb335f03102..fa06c161f139 100644
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -171,10 +171,12 @@ static int tcf_mirred(struct sk_buff *skb, const struct 
tc_action *a,
                      struct tcf_result *res)
 {
        struct tcf_mirred *m = to_mirred(a);
+       struct sk_buff *skb2 = skb;
        bool m_mac_header_xmit;
        struct net_device *dev;
-       struct sk_buff *skb2;
        int retval, err = 0;
+       bool want_ingress;
+       bool is_redirect;
        int m_eaction;
        int mac_len;
 
@@ -196,16 +198,19 @@ static int tcf_mirred(struct sk_buff *skb, const struct 
tc_action *a,
                goto out;
        }
 
-       skb2 = skb_clone(skb, GFP_ATOMIC);
-       if (!skb2)
-               goto out;
+       is_redirect = tcf_mirred_is_act_redirect(m_eaction);
+       if (!skb_at_tc_ingress(skb) || !is_redirect) {
+               skb2 = skb_clone(skb, GFP_ATOMIC);
+               if (!skb2)
+                       goto out;
+       }
 
        /* If action's target direction differs than filter's direction,
         * and devices expect a mac header on xmit, then mac push/pull is
         * needed.
         */
-       if (skb_at_tc_ingress(skb) != tcf_mirred_act_wants_ingress(m_eaction) &&
-           m_mac_header_xmit) {
+       want_ingress = tcf_mirred_act_wants_ingress(m_eaction);
+       if (skb_at_tc_ingress(skb) != want_ingress && m_mac_header_xmit) {
                if (!skb_at_tc_ingress(skb)) {
                        /* caught at egress, act ingress: pull mac */
                        mac_len = skb_network_header(skb) - skb_mac_header(skb);
@@ -216,14 +221,22 @@ static int tcf_mirred(struct sk_buff *skb, const struct 
tc_action *a,
                }
        }
 
+       skb2->skb_iif = skb->dev->ifindex;
+       skb2->dev = dev;
+
        /* mirror is always swallowed */
-       if (tcf_mirred_is_act_redirect(m_eaction)) {
+       if (is_redirect) {
                skb2->tc_redirected = 1;
                skb2->tc_from_ingress = skb2->tc_at_ingress;
+
+               /* let's the caller reinject the packet, if possible */
+               if (skb_at_tc_ingress(skb)) {
+                       res->ingress = want_ingress;
+                       res->qstats = this_cpu_ptr(m->common.cpu_qstats);
+                       return TC_ACT_MIRRED;
+               }
        }
 
-       skb2->skb_iif = skb->dev->ifindex;
-       skb2->dev = dev;
        if (!tcf_mirred_act_wants_ingress(m_eaction))
                err = dev_queue_xmit(skb2);
        else
-- 
2.17.1