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Date:   Wed, 2 Nov 2022 14:25:17 +0100
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Reply-To: nicolas.dichtel@6wind.com
Subject: Re: [PATCH net-next] net: tun: bump the link speed from 10Mbps to
 10Gbps
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To:     Ilya Maximets <i.maximets@ovn.org>, netdev@vger.kernel.org
Cc:     Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Paolo Abeni <pabeni@redhat.com>, linux-kernel@vger.kernel.org
References: <20221031173953.614577-1-i.maximets@ovn.org>
From:   Nicolas Dichtel <nicolas.dichtel@6wind.com>
Organization: 6WIND
In-Reply-To: <20221031173953.614577-1-i.maximets@ovn.org>
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Le 31/10/2022 à 18:39, Ilya Maximets a écrit :
> 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.
> 
> Alternative might be to explicitly report UNKNOWN and let the user
> decide on a right value for them.  And it is indeed "the right way"
> of fixing the problem.  However, that may cause issues with bonding
> or with some userspace applications that may rely on speed value to
> be reported (even though they should not).  Just changing the speed
> value should be a safer option.
> 
> Users can still override the speed with ethtool, if necessary.
> 
> RFC discussion is linked below.
> 
> Link: https://lore.kernel.org/lkml/20221021114921.3705550-1-i.maximets@ovn.org/
> Link: https://mail.openvswitch.org/pipermail/ovs-discuss/2022-July/051958.html
> Signed-off-by: Ilya Maximets <i.maximets@ovn.org>
Reviewed-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>