netdev - Re: [Cake] [PATCH net-next v14 4/7] sch_cake: Add NAT awareness to packet classifier

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Message-ID: <20180521233406.GG26212@localhost.localdomain>
Date:   Mon, 21 May 2018 20:34:06 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     netdev@...r.kernel.org, cake@...ts.bufferbloat.net,
        netfilter-devel@...r.kernel.org
Subject: Re: [Cake] [PATCH net-next v14 4/7] sch_cake: Add NAT awareness to
 packet classifier

[Cc'ing netfilter-devel@ for awareness]

On Mon, May 21, 2018 at 10:35:58PM +0200, Toke Høiland-Jørgensen 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 |   79 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
> index 92623160d43e..04364993ce19 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)
> @@ -516,6 +522,60 @@ 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.
>   */
> @@ -543,6 +603,9 @@ 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.
> @@ -1894,6 +1957,18 @@ static int cake_change(struct Qdisc *sch, struct nlattr *opt,
>  	if (err < 0)
>  		return err;
>  
> +	if (tb[TCA_CAKE_NAT]) {
> +#if IS_REACHABLE(CONFIG_NF_CONNTRACK)
> +		q->flow_mode &= ~CAKE_FLOW_NAT_FLAG;
> +		q->flow_mode |= CAKE_FLOW_NAT_FLAG *
> +			!!nla_get_u32(tb[TCA_CAKE_NAT]);
> +#else
> +		NL_SET_ERR_MSG_ATTR(extack, "No conntrack support in kernel",
> +				    tb[TCA_CAKE_NAT]);
> +		return -EOPNOTSUPP;
> +#endif
> +	}
> +
>  	if (tb[TCA_CAKE_BASE_RATE64])
>  		q->rate_bps = nla_get_u64(tb[TCA_CAKE_BASE_RATE64]);
>  
> @@ -2066,6 +2141,10 @@ 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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