netdev - Re: [PATCH net-next] neighbor: Add protocol attribute

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Message-Id: <20181214.143850.959035060598325128.davem@davemloft.net>
Date:   Fri, 14 Dec 2018 14:38:50 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     dsahern@...il.com
Cc:     eric.dumazet@...il.com, netdev@...r.kernel.org,
        roopa@...ulusnetworks.com
Subject: Re: [PATCH net-next] neighbor: Add protocol attribute

From: David Ahern <dsahern@...il.com>
Date: Tue, 11 Dec 2018 08:22:04 -0700

> On 12/10/18 10:59 PM, David Miller wrote:
>> From: David Ahern <dsahern@...il.com>
>> Date: Mon, 10 Dec 2018 19:47:33 -0700
>> 
>>> On 12/7/18 4:45 PM, David Miller wrote:
>>>>
>>>> Right, neigh->ha[] should probably be kept 8-byte aligned.
>>>>
>>>
>>> From what I can see ha is only used with memcpy, and neighbour struct is
>>> annotated with __randomize_layout. Are you saying that ha should be
>>> marked with __aligned(8)?
>> 
>> People who care about performance probably don't build with randomization
>> enabled, do they?
>> 
>> Even though it uses memcpy() it will be faster if it is 8 byte aligned
>> and we can probably explicitly take advantage of that alignment even
>> more if we add the marking as you suggest perhaps.
>> 
>> Given all of this, what is your opinion?
>> 
> 
> Arguably my take is ethernet centric. I do not see how 8-byte alignment
> matters when copying 6 bytes. In my response to Eric I showed ha is
> still 4-byte aligned and does not straddle cachelines. Those seem the
> more relevant to me.

Ok, please resubmit as-is if you like.