netdev - Re: [net-next] openvswitch: Simplify do_execute

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Date:   Thu, 26 Jan 2017 18:17:41 -0800
From:   Jarno Rajahalme <jarno.rajahalme@...il.com>
To:     Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc:     Andy Zhou <azhou@....org>
Subject: Re: [net-next] openvswitch: Simplify do_execute_actions().

Nice clean-up.

Acked-by: Jarno Rajahalme <jarno@....org>

> On Jan 25, 2017, at 9:24 PM, Andy Zhou <azhou@....org> wrote:
> 
> do_execute_actions() implements a worthwhile optimization: in case
> an output action is the last action in an action list, skb_clone()
> can be avoided by outputing the current skb. However, the
> implementation is more complicated than necessary.  This patch
> simplify this logic.
> 
> Signed-off-by: Andy Zhou <azhou@....org>
> ---
> net/openvswitch/actions.c | 40 +++++++++++++++++++---------------------
> 1 file changed, 19 insertions(+), 21 deletions(-)
> 
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index 514f7bc..3866608 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -830,6 +830,9 @@ static void do_output(struct datapath *dp, struct sk_buff *skb, int out_port,
> {
> 	struct vport *vport = ovs_vport_rcu(dp, out_port);
> 
> +	if (unlikely(!skb))
> +		return;
> +
> 	if (likely(vport)) {
> 		u16 mru = OVS_CB(skb)->mru;
> 		u32 cutlen = OVS_CB(skb)->cutlen;
> @@ -1141,12 +1144,6 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> 			      struct sw_flow_key *key,
> 			      const struct nlattr *attr, int len)
> {
> -	/* Every output action needs a separate clone of 'skb', but the common
> -	 * case is just a single output action, so that doing a clone and
> -	 * then freeing the original skbuff is wasteful.  So the following code
> -	 * is slightly obscure just to avoid that.
> -	 */
> -	int prev_port = -1;
> 	const struct nlattr *a;
> 	int rem;
> 
> @@ -1154,20 +1151,25 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> 	     a = nla_next(a, &rem)) {
> 		int err = 0;
> 
> -		if (unlikely(prev_port != -1)) {
> -			struct sk_buff *out_skb = skb_clone(skb, GFP_ATOMIC);
> +		switch (nla_type(a)) {
> +		case OVS_ACTION_ATTR_OUTPUT: {
> +			int port = nla_get_u32(a);
> 
> -			if (out_skb)
> -				do_output(dp, out_skb, prev_port, key);
> +			/* Every output action needs a separate clone
> +			 * of 'skb', In case the output action is the
> +			 * last action, cloning can be avoided.
> +			 */
> +			if (nla_is_last(a, rem)) {
> +				do_output(dp, skb, port, key);
> +				/* 'skb' has been used for output.
> +				 */
> +				return 0;
> +			}
> 
> +			do_output(dp, skb_clone(skb, GFP_ATOMIC), port, key);
> 			OVS_CB(skb)->cutlen = 0;
> -			prev_port = -1;
> -		}
> -
> -		switch (nla_type(a)) {
> -		case OVS_ACTION_ATTR_OUTPUT:
> -			prev_port = nla_get_u32(a);
> 			break;
> +		}
> 
> 		case OVS_ACTION_ATTR_TRUNC: {
> 			struct ovs_action_trunc *trunc = nla_data(a);
> @@ -1257,11 +1259,7 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> 		}
> 	}
> 
> -	if (prev_port != -1)
> -		do_output(dp, skb, prev_port, key);
> -	else
> -		consume_skb(skb);
> -
> +	consume_skb(skb);
> 	return 0;
> }
> 
> -- 
> 1.8.3.1
>