Re: [patch v4, kernel version 3.2.1] net/ipv4/ip_gre: Ethernetmultipoint GRE over IP

[Jesse Gross]

On Thu, Jan 26, 2012 at 9:59 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> Le vendredi 27 janvier 2012 Ã 09:24 +1100, Joseph Glanville a Ãcrit :
>> David is correct, the forwarding speed of Open vSwitch is at parity
>> with the Linux Bridging module and its tunneling speed is actually
>> slightly faster than the in kernel GRE implementation. I have tested
>> this across a variety of configurations.
>
> Thanks for this input ! When was this tested exactly, and do you have
> some "perf tool" reports to provide ?
>
> GRE is lockless since one year or so (modulo how is setup the tunnel as
> discovered recently)

The out-of-tree OVS GRE stack (which is separate for practical and
historical reasons but I would like to combine with the in-kernel one
in the future) uses a few dirty tricks to help performance.  I don't
know the parameters that Joseph used to test but one that he might be
benefiting from here is where we cache the full set of headers to be
pushed (GRE/IP/Ethernet) as well any routing/switching decisions.
This turns a GRE encapsulation into a simple memcpy if there is enough
headroom.  It's not something that I would want to propose for more
general usage but I think that GSO/GRO for GRE would get at least some
of that benefit and would also make things easier when NICs with
support for encapsulated offloads start showing up.
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