Re: [PATCH net-next v3 5/5] act_mirred: use TC_ACT_REINJECT when possible

[Jiri Pirko <jiri@resnulli.us>]

Tue, Jul 24, 2018 at 10:06:43PM CEST, pabeni@redhat.com wrote:
>When mirred is invoked from the ingress path, and it wants to redirect
>the processed packet, it can now use the TC_ACT_REINJECT 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 openvswitch datapath.
>
>v1 -> v2: use ACT_MIRRED instead of ACT_REDIRECT
>v2 -> v3: updated after action rename, fixed a typo into the commit
>	message
>
>Signed-off-by: Paolo Abeni <pabeni@redhat.com>
>---
> net/sched/act_mirred.c | 34 ++++++++++++++++++++++++----------
> 1 file changed, 24 insertions(+), 10 deletions(-)
>
>diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
>index eeb335f03102..368187312136 100644
>--- a/net/sched/act_mirred.c
>+++ b/net/sched/act_mirred.c
>@@ -25,6 +25,7 @@
> #include <net/net_namespace.h>
> #include <net/netlink.h>
> #include <net/pkt_sched.h>
>+#include <net/pkt_cls.h>
> #include <linux/tc_act/tc_mirred.h>
> #include <net/tc_act/tc_mirred.h>
> 
>@@ -171,10 +172,12 @@ 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 +199,19 @@ 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);
>@@ -216,15 +222,23 @@ 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)) {

I probably missed something. Why only on ingress?

The patch looks good to me.


>+			res->ingress = want_ingress;
>+			res->qstats = this_cpu_ptr(m->common.cpu_qstats);
>+			return TC_ACT_REINJECT;
>+		}
> 	}
> 
>-	skb2->skb_iif = skb->dev->ifindex;
>-	skb2->dev = dev;
>-	if (!tcf_mirred_act_wants_ingress(m_eaction))
>+	if (!want_ingress)
> 		err = dev_queue_xmit(skb2);
> 	else
> 		err = netif_receive_skb(skb2);
>-- 
>2.17.1
>