netdev - Re: [PATCH net-next] net: openvswitch: Set OvS recirc

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Date:   Mon, 19 Aug 2019 14:42:41 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Paul Blakey <paulb@...lanox.com>
Cc:     Pravin B Shelar <pshelar@....org>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Justin Pettit <jpettit@...ira.com>,
        Simon Horman <simon.horman@...ronome.com>,
        Vlad Buslov <vladbu@...lanox.com>,
        Jiri Pirko <jiri@...lanox.com>, Roi Dayan <roid@...lanox.com>,
        Yossi Kuperman <yossiku@...lanox.com>,
        Rony Efraim <ronye@...lanox.com>, Oz Shlomo <ozsh@...lanox.com>
Subject: Re: [PATCH net-next] net: openvswitch: Set OvS recirc_id from tc
 chain

On Sun, Aug 18, 2019 at 07:00:59PM +0300, Paul Blakey wrote:
> What do you guys say about the following diff on top of the last one?
> Use static key, and also have OVS_DP_CMD_SET command probe/enable the feature.
> 
> This will allow userspace to probe the feature, and selectivly enable it via the
> OVS_DP_CMD_SET command.

I'm not convinced yet that we need something like this. Been
wondering, skb_ext_find() below is not that expensive if not in use.
It's just a bit check and that's it, it returns NULL.

And drivers will only be setting this if they have tc-offloading
enabled (assuming they won't be seeing it for chain 0 all the time).
On which case, with tc offloading, we need this in order to work
properly.

Is the bit checking really that worrysome?

> --- a/net/openvswitch/flow.c
> +++ b/net/openvswitch/flow.c
> @@ -853,8 +853,10 @@ int ovs_flow_key_extract(const struct ip_tunnel_info *tun_info,
>  	key->mac_proto = res;
>  
>  #if IS_ENABLED(CONFIG_NET_TC_SKB_EXT)
> -	tc_ext = skb_ext_find(skb, TC_SKB_EXT);
> -	key->recirc_id = tc_ext ? tc_ext->chain : 0;
> +	if (static_branch_unlikely(&tc_recirc_sharing_support)) {
> +		tc_ext = skb_ext_find(skb, TC_SKB_EXT);
> +		key->recirc_id = tc_ext ? tc_ext->chain : 0;
> +	}
>  #else
>  	key->recirc_id = 0;
>  #endif
> -- 
> 1.8.3.1
>