Locate power-hungry USB device seen in powertop

Question

The battery life on my Dell XPS 13, while never great, has gotten seriously bad lately. Using powertop, I've noticed that there seems to be some sort of USB device drawing quite a bit of power.

PowerTOP 2.6.1    Overview   Idle stats   Frequency stats   Device stats   Tunables                                     

The battery reports a discharge rate of 12.8 W
The estimated remaining time is 2 hours, 2 minutes

Summary: 377.0 wakeups/second,  47.0 GPU ops/seconds, 0.0 VFS ops/sec and 6.0% CPU use

Power est.              Usage       Events/s    Category       Description
  3.85 W    100.0%                      Device         USB device: usb-device-0cf3-3004
  3.58 W     40.0%                      Device         Display backlight
  1.81 W      2.5 ms/s     130.5        Interrupt      PS/2 Touchpad / Keyboard / Mouse
  1.13 W     17.5 ms/s     118.4        Process        compiz
  452 mW     16.0 ms/s      31.0        Process        /usr/bin/X -core :0 -seat seat0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch
  419 mW      9.4 ms/s      32.5        Process        /usr/lib/gnome-terminal/gnome-terminal-server --app-id com.canonical.Terminal.swYIftfwqqbunjqoezwSzqxRaqPBMBqC
  315 mW    676.0 µs/s      22.6        Interrupt      [26] i915
  294 mW      0.0 pkts/s                Device         nic:virbr0
  165 mW      0.0 pkts/s                Device         nic:lxcbr0
  144 mW    628.1 µs/s      10.3        Process        nautilus -n
  129 mW    111.7 µs/s       9.3        Process        [rcu_sched]
  112 mW      2.7 ms/s       7.5        Process        /usr/bin/ibus-daemon --daemonize --xim

Problem is, I don't have any USB devices plugged into the laptop.

What would be my next step for figuring out how to identify the USB device using all this power?

EDIT:

Further research led me to run lsusb which shows the following output:

Bus 004 Device 003: ID 0cf3:3004 Atheros Communications, Inc. 
Bus 004 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 004 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 003: ID 1bcf:288f Sunplus Innovation Technology Inc. 
Bus 003 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

And some Google searching suggests that the problem device is related to my WiFi/Bluetooth module. Most of the forum posts I've found suggest that there used to be a problem with the drivers for this device but that if you're running the latest version of Ubuntu you should be good. I'm on Ubuntu 15.04 but still having problems so I'm not sure what my next step should be.

Answer 1

You need to enable USB autosuspend mode for the bluetooth device.

I suggest to install TLP to achieve this. TLP's default configuration will enable autosuspend for all USB devices except (externally attached) mice and keyboards.

In case you don't use bluetooth at all, you may even disable it at boot time by enabling the following line in TLP's configuration:

    DEVICES_TO_DISABLE_ON_STARTUP="bluetooth"

Btw: the XPS13 2015 Ubuntu 14.04 factory install contains TLP.