netdev - Re: [PATCH net-next v3 5/5] act_mirred: use TC_ACT

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Date:   Wed, 25 Jul 2018 16:04:03 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Eyal Birger <eyal.birger@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next v3 5/5] act_mirred: use TC_ACT_REINJECT when
 possible

On Wed, 2018-07-25 at 15:52 +0200, Jiri Pirko wrote:
> Tue, Jul 24, 2018 at 10:06:43PM CEST, pabeni@...hat.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@...hat.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?

To keep the implementation as simple as possible: if I read correctly,
it is impossible for a filter detect if called by the clsact or the dev
root qdisc, and I think we could safely avoid the skb clone with a not
invasive patch, only if called from the clsact.

[please let me know if the above is somewhat clear ;)]

Also this covers nicely the relevant use case (TC S/W datapath).

Thanks,

Paolo