Power Management And Tuning A Thinkpad X230t

I’m presenting some power tuning measurements for an X230 tablet, potentially to compare against other systems (and to see if your own power use is minimized):

System Configuration:

• X230 tablet, i5-3320M CPU, 8 GB RAM, Crucial M4 128 GB SSD
• Running up-to-date Xubuntu 16.04, with Intel microcode and power tuning by TLP, running on Ext4 filesystem, XFCE Display Compositing OFF (reduce GPU use)
• Measurements taken using powertop 2.8, pre-calibrated

Power Scenarios:

Reader Mode – mostly idle, Chrome not running, WiFi off (hardware switch), display brightness one notch above minimum (minimum usable indoors), bluetooth off:

• Battery drain 7.3-7.8W
• 4.4W – Base system use (mistakenly attributed to the wired ethernet due to a glitch in calibration approach) – motherboard, RAM, etc
• 2.2W – Display backlight
• 0 – 400 mW – Touchscreen

Reader with WiFi & Chrome on – mostly idle, Chrome open with a few idle tabs, WiFi on but not being used.  In tablet mode (keyboard/mouse inactive), reading locally stored comics in Comix, bluetooth off

• Battery drain 8.6-9.1W
• 4.16W – Base system use
• 2.4W – Display backlight
• 852 mW – 963 mW CPU (combined, 1-1.4% use)
  • 627-734 mW – CPU core
  • 225-229 mW – CPU misc
• 442-448 mW – Wireless, 3-10 packets per second
• 40-50 mW – GPU combined use (half core, half misc)

Normal range when web browsing:

• 10-12W, although real battery life is 4-5 hours on 62.7 Wh 6-cell battery

Playing back H264 1080p video in SMPlayer Using VAAPI for Graphics Acceleration:

• 16.7W, 6-7% CPU use, but mostly active GPU

Conclusions:

You’re not going to get much under 7W of power draw, or 8.8 hours of use (at least not under Linux).  A more realistic estimate under normal use is about 12-14W of power draw, giving 4-5 hours of battery.  Most of the difference from base use will be CPU & GPU use, even in a mostly-idle state, with the network card making a lesser contribution.

By way of comparison, I get a minimum of about 8.75W with a very similarly configured Thinkpad T530 with an i5-3210M CPU, the HD+ 1600 x 900 screen, and screen brightness around 40-50%.  That’s about as dim as it will be usable.

It is very difficult to make the a system power efficient with the 35W TDP CPUs, at least not by modern standards.  It’s not uncommon to see modern 14/15″ laptops idling at under 10W, even with larger full-HD screens and sometimes quad-core CPUs.