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Date:   Wed, 16 May 2018 23:14:44 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Cong Wang <xiyou.wangcong@...il.com>
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

Cong Wang <xiyou.wangcong@...il.com> writes:

> 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.

Good point, will fix :)

-Toke

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