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Date:   Wed, 16 May 2018 13:56:59 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Cake List <cake@...ts.bufferbloat.net>
Subject: Re: [PATCH net-next v12 4/7] sch_cake: Add NAT awareness to packet classifier

On Wed, May 16, 2018 at 1:29 PM, Toke Høiland-Jørgensen <toke@...e.dk> wrote:
> When CAKE is deployed on a gateway that also performs NAT (which is a
> common deployment mode), the host fairness mechanism cannot distinguish
> internal hosts from each other, and so fails to work correctly.
>
> To fix this, we add an optional NAT awareness mode, which will query the
> kernel conntrack mechanism to obtain the pre-NAT addresses for each packet
> and use that in the flow and host hashing.
>
> When the shaper is enabled and the host is already performing NAT, the cost
> of this lookup is negligible. However, in unlimited mode with no NAT being
> performed, there is a significant CPU cost at higher bandwidths. For this
> reason, the feature is turned off by default.
>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>
> ---
>  net/sched/sch_cake.c |   73 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 73 insertions(+)
>
> diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
> index 65439b643c92..e1038a7b6686 100644
> --- a/net/sched/sch_cake.c
> +++ b/net/sched/sch_cake.c
> @@ -71,6 +71,12 @@
>  #include <net/tcp.h>
>  #include <net/flow_dissector.h>
>
> +#if IS_REACHABLE(CONFIG_NF_CONNTRACK)
> +#include <net/netfilter/nf_conntrack_core.h>
> +#include <net/netfilter/nf_conntrack_zones.h>
> +#include <net/netfilter/nf_conntrack.h>
> +#endif
> +
>  #define CAKE_SET_WAYS (8)
>  #define CAKE_MAX_TINS (8)
>  #define CAKE_QUEUES (1024)
> @@ -514,6 +520,60 @@ static bool cobalt_should_drop(struct cobalt_vars *vars,
>         return drop;
>  }
>
> +#if IS_REACHABLE(CONFIG_NF_CONNTRACK)
> +
> +static void cake_update_flowkeys(struct flow_keys *keys,
> +                                const struct sk_buff *skb)
> +{
> +       const struct nf_conntrack_tuple *tuple;
> +       enum ip_conntrack_info ctinfo;
> +       struct nf_conn *ct;
> +       bool rev = false;
> +
> +       if (tc_skb_protocol(skb) != htons(ETH_P_IP))
> +               return;
> +
> +       ct = nf_ct_get(skb, &ctinfo);
> +       if (ct) {
> +               tuple = nf_ct_tuple(ct, CTINFO2DIR(ctinfo));
> +       } else {
> +               const struct nf_conntrack_tuple_hash *hash;
> +               struct nf_conntrack_tuple srctuple;
> +
> +               if (!nf_ct_get_tuplepr(skb, skb_network_offset(skb),
> +                                      NFPROTO_IPV4, dev_net(skb->dev),
> +                                      &srctuple))
> +                       return;
> +
> +               hash = nf_conntrack_find_get(dev_net(skb->dev),
> +                                            &nf_ct_zone_dflt,
> +                                            &srctuple);
> +               if (!hash)
> +                       return;
> +
> +               rev = true;
> +               ct = nf_ct_tuplehash_to_ctrack(hash);
> +               tuple = nf_ct_tuple(ct, !hash->tuple.dst.dir);
> +       }
> +
> +       keys->addrs.v4addrs.src = rev ? tuple->dst.u3.ip : tuple->src.u3.ip;
> +       keys->addrs.v4addrs.dst = rev ? tuple->src.u3.ip : tuple->dst.u3.ip;
> +
> +       if (keys->ports.ports) {
> +               keys->ports.src = rev ? tuple->dst.u.all : tuple->src.u.all;
> +               keys->ports.dst = rev ? tuple->src.u.all : tuple->dst.u.all;
> +       }
> +       if (rev)
> +               nf_ct_put(ct);
> +}
> +#else
> +static void cake_update_flowkeys(struct flow_keys *keys,
> +                                const struct sk_buff *skb)
> +{
> +       /* There is nothing we can do here without CONNTRACK */
> +}
> +#endif
> +
>  /* Cake has several subtle multiple bit settings. In these cases you
>   *  would be matching triple isolate mode as well.
>   */
> @@ -541,6 +601,9 @@ static u32 cake_hash(struct cake_tin_data *q, const struct sk_buff *skb,
>         skb_flow_dissect_flow_keys(skb, &keys,
>                                    FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
>
> +       if (flow_mode & CAKE_FLOW_NAT_FLAG)
> +               cake_update_flowkeys(&keys, skb);
> +
>         /* flow_hash_from_keys() sorts the addresses by value, so we have
>          * to preserve their order in a separate data structure to treat
>          * src and dst host addresses as independently selectable.
> @@ -1727,6 +1790,12 @@ static int cake_change(struct Qdisc *sch, struct nlattr *opt,
>                 q->flow_mode = (nla_get_u32(tb[TCA_CAKE_FLOW_MODE]) &
>                                 CAKE_FLOW_MASK);
>
> +       if (tb[TCA_CAKE_NAT]) {
> +               q->flow_mode &= ~CAKE_FLOW_NAT_FLAG;
> +               q->flow_mode |= CAKE_FLOW_NAT_FLAG *
> +                       !!nla_get_u32(tb[TCA_CAKE_NAT]);
> +       }


I think it's better to return -EOPNOTSUPP when CONFIG_NF_CONNTRACK
is not enabled.


> +
>         if (tb[TCA_CAKE_RTT]) {
>                 q->interval = nla_get_u32(tb[TCA_CAKE_RTT]);
>
> @@ -1892,6 +1961,10 @@ static int cake_dump(struct Qdisc *sch, struct sk_buff *skb)
>         if (nla_put_u32(skb, TCA_CAKE_ACK_FILTER, q->ack_filter))
>                 goto nla_put_failure;
>
> +       if (nla_put_u32(skb, TCA_CAKE_NAT,
> +                       !!(q->flow_mode & CAKE_FLOW_NAT_FLAG)))
> +               goto nla_put_failure;
> +
>         return nla_nest_end(skb, opts);
>
>  nla_put_failure:
>

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