netdev - Re: [PATCH v3 1/2] core: Factor out flow calculation from get_rps

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Date:	Tue, 3 Aug 2010 15:18:40 +0800
From:	Changli Gao <xiaosuo@...il.com>
To:	Krishna Kumar2 <krkumar2@...ibm.com>
Cc:	arnd@...db.de, bhutchings@...arflare.com, davem@...emloft.net,
	mst@...hat.com, netdev@...r.kernel.org, therbert@...gle.com
Subject: Re: [PATCH v3 1/2] core: Factor out flow calculation from get_rps_cpu

On Tue, Aug 3, 2010 at 2:11 PM, Changli Gao <xiaosuo@...il.com> wrote:
> On Tue, Aug 3, 2010 at 1:57 PM, Krishna Kumar2 <krkumar2@...ibm.com> wrote:
>> Hi Changli,
>>
>> Good catch.
>>
>> Instead of adding support for ethernet header or pull/push,
>> I could defer the skb_push(ETH_HLEN), something like:
>>
>> static int macvtap_forward(struct net_device *dev, struct sk_buff *skb)
>> {
>>        struct macvtap_queue *q = macvtap_get_queue(dev, skb);
>>        if (!q)
>>                goto drop;
>>
>>        if (skb_queue_len(&q->sk.sk_receive_queue) >= dev->tx_queue_len)
>>                goto drop;
>>
>> +       skb_push(skb, ETH_HLEN);
>>        ...
>> }
>>
>> and remove the same in macvtap_receive. Will this be better?
>>
>
> I am confused by the call sites of macvlan_dev.receive and
> macvlan_dev.forward. They both are possible to be called in both
> RX(skb->data points to network header) and TX(skb->data points to
> ethernet) paths. The current code in macvtap shows that
> macvlan_dev.receive should be called in network layer, and
> macvlan_dev.forward should be called in dev layer. Am I correct?
>

After checking the code carefully, I find macvlan_dev.receive is
called in network layer(RX path), and macvlan_dev.forward is called in
dev layer(TX path). The current code hasn't any issue. Your solution
won't work, as macvtap_forward is called in dev layer, when skb->data
points to ethernet header already.

-- 
Regards,
Changli Gao(xiaosuo@...il.com)
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