Re: [RFE net-next] net: tun: 1000x speed up

From: Ilya Maximets
Date: Mon Oct 31 2022 - 13:10:08 EST


On 10/21/22 13:49, Ilya Maximets wrote:
> The 10Mbps link speed was set in 2004 when the ethtool interface was
> initially added to the tun driver. It might have been a good
> assumption 18 years ago, but CPUs and network stack came a long way
> since then.
>
> Other virtual ports typically report much higher speeds. For example,
> veth reports 10Gbps since its introduction in 2007.
>
> Some userspace applications rely on the current link speed in
> certain situations. For example, Open vSwitch is using link speed
> as an upper bound for QoS configuration if user didn't specify the
> maximum rate. Advertised 10Mbps doesn't match reality in a modern
> world, so users have to always manually override the value with
> something more sensible to avoid configuration issues, e.g. limiting
> the traffic too much. This also creates additional confusion among
> users.
>
> Bump the advertised speed to at least match the veth. 10Gbps also
> seems like a more or less fair assumption these days, even though
> CPUs can do more. Alternative might be to explicitly report UNKNOWN
> and let the application/user decide on a right value for them.
>
> Link: https://mail.openvswitch.org/pipermail/ovs-discuss/2022-July/051958.html
> Signed-off-by: Ilya Maximets <i.maximets@xxxxxxx>
> ---
>
> Sorry for the clickbait subject line. Can change it to something more
> sensible while posting non-RFE patch. Something like:
>
> 'net: tun: bump the link speed from 10Mbps to 10Gbps'
>
> This patch is RFE just to start a conversation.

OK. There seems to be no more discussions around the topic, so
I'll make a conclusion.

General understanding is that reporting UNKNOWN will cause problems
with bonding (not sure why anyone will add tap into bonding outside
of just for testing reasons, but that's a different topic) and will
potentially cause problems with userpsace applications that do not
handle that case for some reason. So, this is a risky option at the
moment.

There was no strong opinion against equalizing speeds between veth
and tun/tap. Sounds like a safe option in general and there are no
known use cases that will be negatively affected.

So, I think, I'll go ahead and post the non-RFC version of the
proposed change.

Thanks!

Best regards, Ilya Maximets.