linux-kernel - Realtek NIC uses over 1 Watt with no traffic

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Date:   Tue, 20 Nov 2018 09:40:25 +0100
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Realtek linux nic maintainers <nic_swsd@...ltek.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Realtek NIC uses over 1 Watt with no traffic

Dear Linux folks,

Using Ubuntu 18.10, Linux 4.18.0-11-generic, PowerTOP 2.9 shows, the NIC 
uses 1.77 Watts. A network cable is plugged in, but there is no real 
traffic according to `iftop`. Only an email program is running.

     $ lspci -nn -s 3:00.1
     03:00.1 Ethernet controller [0200]: Realtek Semiconductor Co., Ltd. 
RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller [10ec:8168] 
(rev 12)

Is that a measurement error, or does the NIC really need that much power?

> Der Akku meldet eine Entladungsrate von 10.2 W
> Der verbrauchte Strom ist: 0.00 J
> Grundsätzlich benötigte Energie wird auf 10.5 W geschätzt
> 
> Energieschätz.    Auslastung     Gerätename
>   7.03 W      4,9%        Display backlight
>   1.77 W      0,0 pkts/s  Netzwerkschnittstelle: enp3s0f1(r8169)

Letting it run for a while, the value even grows to 3.5 Watts, but
closing and starting PowerTOP, it goes back to 1.7X Watts.

Kind regards,

Paul