netdev - Re: [PATCH 1/3] vlan: Do not support clearing VLAN_FLAG_REORDER

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Message-ID: <BANLkTikxNNpaXSkNaf6b2GHgaEZQ5HiO2g@mail.gmail.com>
Date:	Tue, 24 May 2011 09:44:42 +0200
From:	Michał Mirosław <mirqus@...il.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	Ben Greear <greearb@...delatech.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	David Miller <davem@...emloft.net>,
	shemminger@...ux-foundation.org, jpirko@...hat.com,
	xiaosuo@...il.com, netdev@...r.kernel.org, kaber@...sh.net,
	fubar@...ibm.com, eric.dumazet@...il.com, andy@...yhouse.net,
	jesse@...ira.com
Subject: Re: [PATCH 1/3] vlan: Do not support clearing VLAN_FLAG_REORDER_HDR

2011/5/24 Nicolas de Pesloüan <nicolas.2p.debian@...il.com>:
>> If it turns out the NIC is not stripping VLAN tags for whatever reason,
>> we might be able to optimize things so that it never does the HW emulation
>> so that it never has to un-do it later.
> It might be very tricky to avoid any do-undo-redo situation. I will latter
> try and describe all the possible situations: with/without hw-accel,
> with/without a protocol handler registered on the parent interface,
> with/without a child interface build on top of a particular parent interface
> and with the corresponding VLAN ID...

Hardware tag stripping could be disabled whenever AF_PACKET listener
is present on the base interface. It should be easy now with the new
features handling.

BTW, what's the performance gain from hw tag stripping? Besides saving
12-byte memmove() in one cacheline?

Best Regards,
Michał Mirosław
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