netdev - Re: [patch net-next-2.6 V3] net: convert bonding to use rx

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Message-ID: <4D683F6D.1030208@gmail.com>
Date:	Sat, 26 Feb 2011 00:46:53 +0100
From:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
To:	Jiri Pirko <jpirko@...hat.com>
CC:	David Miller <davem@...emloft.net>, kaber@...sh.net,
	eric.dumazet@...il.com, netdev@...r.kernel.org,
	shemminger@...ux-foundation.org, fubar@...ibm.com,
	andy@...yhouse.net
Subject: Re: [patch net-next-2.6 V3] net: convert bonding to use rx_handler

Le 23/02/2011 20:05, Jiri Pirko a écrit :
> This patch converts bonding to use rx_handler. Results in cleaner
> __netif_receive_skb() with much less exceptions needed. Also
> bond-specific work is moved into bond code.
>
> Did performance test using pktgen and counting incoming packets by
> iptables. No regression noted.
>
> Signed-off-by: Jiri Pirko<jpirko@...hat.com>
>
> v1->v2:
>          using skb_iif instead of new input_dev to remember original
> 	device
>
> v2->v3:
> 	do another loop in case skb->dev is changed. That way orig_dev
> 	core can be left untouched.

Hi Jiri,

Eventually taking enough time for a review.

I think we should split this change :

1/ Change __netif_receive_skb() to call rx_handler for diverted net_device, until rx_handler is NULL.

2/ Convert currently existing rx_handlers (bridge and macvlan) to use this new "loop" feature, 
removing the need to call netif_rx() inside their respective rx_handler and also removing the 
associated overhead.

3/ Convert bonding to use rx_handlers.

Also, on step 1, we definitely need to clarify what orig_dev should be.

I now think that orig_dev should be "the device one level below the current one" or NULL if current 
device was not diverted from another one. It means that we should keep an array of crossed 
(diverted) devices and the associated orig_dev. This array would be used to pass the right orig_dev 
to protocol handlers, depending on the device they register on :

eth0 -> bond0 -> br0

A protocol handler registered on bond0 would receive eth0 as orig_dev.
A protocol handler registered on br0 would receive bond0 as orig_dev.

[snip]

> @@ -3167,32 +3135,8 @@ static int __netif_receive_skb(struct sk_buff *skb)

[snip]

> +another_round:
> +
> +	__this_cpu_inc(softnet_data.processed);
> +
>   #ifdef CONFIG_NET_CLS_ACT
>   	if (skb->tc_verd&  TC_NCLS) {
>   		skb->tc_verd = CLR_TC_NCLS(skb->tc_verd);
> @@ -3209,8 +3157,7 @@ static int __netif_receive_skb(struct sk_buff *skb)
>   #endif
>
>   	list_for_each_entry_rcu(ptype,&ptype_all, list) {
> -		if (ptype->dev == null_or_orig || ptype->dev == skb->dev ||
> -		    ptype->dev == orig_dev) {
> +		if (!ptype->dev || ptype->dev == skb->dev) {
>   			if (pt_prev)
>   				ret = deliver_skb(skb, pt_prev, orig_dev);
>   			pt_prev = ptype;
> @@ -3224,16 +3171,20 @@ static int __netif_receive_skb(struct sk_buff *skb)
>   ncls:
>   #endif
>

Why do you loop to ptype_all before calling rx_handler ?

I don't understand why ptype_all and ptype_base are not handled at the same place in current 
__netif_receive_skb() but I think we should take the opportunity to change that, unless someone know 
of a good reason not to do so.

> -	/* Handle special case of bridge or macvlan */
>   	rx_handler = rcu_dereference(skb->dev->rx_handler);
>   	if (rx_handler) {

	Nicolas.
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