Subject: Re: [PATCH net-next] vlan: use ether_addr_equal_64bits to instead of ether_addr_equal

From: Ding Tianhong <[email-masked]>
Date: Mon, 3 Mar 2014 14:05:15 +0800

On 2014/3/3 12:36, Joe Perches wrote:
> (adding Jiri Pirko to cc's)
> 
> On Mon, 2014-03-03 at 10:49 +0800, Ding Tianhong wrote:
>> On 2014/3/3 9:49, Joe Perches wrote:
>>> On Mon, 2014-03-03 at 09:14 +0800, Ding Tianhong wrote:
>>>> Ether_addr_equal_64bits is more efficient than ether_addr_equal, and
>>>> can be used when each argument is an array within a structure that
>>>> contains at least two bytes of data beyond the array, so it is safe
>>>> to use it for vlan.
>>> []
>>>> diff --git a/net/8021q/vlan_core.c b/net/8021q/vlan_core.c
>>> []
>>>> @@ -26,7 +26,7 @@ bool vlan_do_receive(struct sk_buff **skbp)
>>>>  		/* Our lower layer thinks this is not local, let's make sure.
>>>>  		 * This allows the VLAN to have a different MAC than the
>>>>  		 * underlying device, and still route correctly. */
>>>> -		if (ether_addr_equal(eth_hdr(skb)->h_dest, vlan_dev->dev_addr))
>>>> +		if (ether_addr_equal_64bits(eth_hdr(skb)->h_dest, vlan_dev->dev_addr))
>>>>  			skb->pkt_type = PACKET_HOST;
>>>>  	}
>>>
>>> Hi again Ding
>>>
>>> If you do have performance numbers:
>>>
>>> The lines above this ether_addr_equal_64 are:
>>>
>>> 	if (skb->pkt_type == PACKET_OTHERHOST) {
>>> 		/* Our lower layer thinks this is not local, let's make sure.
>>> 		 * This allows the VLAN to have a different MAC than the
>>> 		 * underlying device, and still route correctly. */
>>> 		if (ether_addr_equal(eth_hdr(skb)->h_dest, vlan_dev->dev_addr))
>>> 			skb->pkt_type = PACKET_HOST;
>>> 	}
>>>
>>> Maybe it'd be faster overall to add an unlikely
>>> to the == test
>>>
>>> 	if (unlikely(skb->pkt_type == PACKET_OTHERHOST)) {
>>
>> Sorry, I can't understand it clearly, do you mean that if the skb deliver to the vlan dev,
>> it is impossible that the pkt_type is PACKET_OTHERHOST at most time?
> 
> No, just that it's maybe better to add an unlikely
> to the test.
> 
> Jiri Pirko's commit 0b5c9db1b modified the code
> from a switch/case to a specific test.
> 
> I don't know how likely it is in normal uses for
> a packet to be delivered as PACKET_OTHERHOST.
> 
> I just hoped that if you in fact had performance
> numbers for your suggested ether_addr_equal_64bits
> test, you might be able to run those same tests
> with if (unlikely(skb->pkt_type == PACKET_OTHERHOST))
> and see if that was better or worse for performance.
> 
> cheers, Joe
> 

OK, I got it and I will review the commit 0b5c9db1b, try to
see the performance.

Regards
Ding

> 
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