netdev - Re: L2 network namespace benchmarking

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Date:	Wed, 28 Mar 2007 06:06:19 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Kirill Korotaev <dev@...ru>
Cc:	Daniel Lezcano <dlezcano@...ibm.com>,
	Linux Containers <containers@...ts.osdl.org>,
	netdev@...r.kernel.org, Dmitry Mishin <dim@...nvz.org>
Subject: Re: L2 network namespace benchmarking

Kirill Korotaev <dev@...ru> writes:

>> Ideally we can optimize the bridge code or something equivalent to
>> it so that we can take one look at the destination mac address and
>> know which network namespace we should be in.  Potentially moving this
>> work to hardware when the hardware supports multiple queues.
> yes, we can hack the bridge, so that packets coming out of eth devices
> can go directly to the container and get out of veth devices from
> inside the container.
>
>> If we can get the overhead out of the routing code that would be
>> tremendous.  However I think it may be more realistic to get the
>> overhead out of the ethernet bridging code where we know we don't need
>> to modify the packet.
> Why not optimize both? :)

If the optimizations are safe and correct I don't have a problem.

When we seem to have multiple copies of a packet in circulation and
we skip a what appears to be a required copy on write, I'm dubious.

Although the more I look at suggested optimization the less dubious I
am as it appears all we are skipping is a ttl decrement and the cow
flag exclusively applies to the data chunk and not the header chunk of
the packet whatever that means.

However we still need to guard against a loop in our routing table
setup between multiple guests.

Eric
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