netdev - Re: [PATCH net-next RFC] net: increase LL_MAX

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Message-ID: <87k2rpwh7m.fsf@vitty.brq.redhat.com>
Date:	Thu, 17 Sep 2015 11:03:25 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	David.Laight@...LAB.COM, haiyangz@...rosoft.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kys@...rosoft.com, jasowang@...hat.com
Subject: Re: [PATCH net-next RFC] net: increase LL_MAX_HEADER for Hyper-V

David Miller <davem@...emloft.net> writes:

> From: David Laight <David.Laight@...LAB.COM>
> Date: Wed, 16 Sep 2015 16:25:03 +0000
>
>> Am I right in thinking this is adding an extra 96 unused bytes to the front
>> of almost all skb just so that hyper-v can make its link level header
>> contiguous with whatever follows (IP header ?).
>> 
>> Doesn't sound ideal.
>
> Agreed, this is rediculous, and the entire stack will incur this cost
> just because hyperv is enabled in the kernel config.

That's what 'RFC' in the subject was about :-)

We already have a precedent of increasing LL_MAX_HEADER globaly because
of a config option (CONFIG_MAC80211_MESH) but Hyper-V needs more.

-- 
  Vitaly
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