netdev - Re: [PATCH net-next v16 5/8] sch_cake: Add NAT awareness to packet classifier

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Message-ID: <20180528195101.7mceghxngz5jhawa@salvia>
Date:   Mon, 28 May 2018 21:51:01 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     netdev@...r.kernel.org, cake@...ts.bufferbloat.net,
        netfilter-devel@...r.kernel.org
Subject: Re: [PATCH net-next v16 5/8] sch_cake: Add NAT awareness to packet
 classifier

On Mon, May 28, 2018 at 04:27:46PM +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.
> 
> Cc: netfilter-devel@...r.kernel.org
> Signed-off-by: Toke Høiland-Jørgensen <toke@...e.dk>
> ---
>  net/sched/sch_cake.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
> 
> diff --git a/net/sched/sch_cake.c b/net/sched/sch_cake.c
> index 68ac908470f1..fecd9caac0cc 100644
> --- a/net/sched/sch_cake.c
> +++ b/net/sched/sch_cake.c
> @@ -71,6 +71,10 @@
>  #include <net/tcp.h>
>  #include <net/flow_dissector.h>
>  
> +#if IS_ENABLED(CONFIG_NF_CONNTRACK)
> +#include <net/netfilter/nf_conntrack_core.h>
> +#endif
> +
>  #define CAKE_SET_WAYS (8)
>  #define CAKE_MAX_TINS (8)
>  #define CAKE_QUEUES (1024)
> @@ -516,6 +520,29 @@ static bool cobalt_should_drop(struct cobalt_vars *vars,
>  	return drop;
>  }
>  
> +static void cake_update_flowkeys(struct flow_keys *keys,
> +				 const struct sk_buff *skb)
> +{
> +#if IS_ENABLED(CONFIG_NF_CONNTRACK)

I would remove the ifdef, not really needed, it will simplify things.

But I leave it to you to decide, this is not I deal breaker.