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

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Date:   Fri, 21 Oct 2022 13:50:45 +0200
From:   Ilya Maximets <i.maximets@....org>
To:     netdev@...r.kernel.org
Cc:     i.maximets@....org, Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [RFE net-next] net: tun: 1000x speed up

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@....org>
> ---
> 
> 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.


Ugh, s/RFE/RFC/ .

> 
>  drivers/net/tun.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/tun.c b/drivers/net/tun.c
> index 27c6d235cbda..48bb4a166ad4 100644
> --- a/drivers/net/tun.c
> +++ b/drivers/net/tun.c
> @@ -3514,7 +3514,7 @@ static void tun_default_link_ksettings(struct net_device *dev,
>  {
>  	ethtool_link_ksettings_zero_link_mode(cmd, supported);
>  	ethtool_link_ksettings_zero_link_mode(cmd, advertising);
> -	cmd->base.speed		= SPEED_10;
> +	cmd->base.speed		= SPEED_10000;
>  	cmd->base.duplex	= DUPLEX_FULL;
>  	cmd->base.port		= PORT_TP;
>  	cmd->base.phy_address	= 0;