F17/F18 simple power consumption comparison on Lenovo T520

Fedora 18 is out and I had spare Lenovo ThinkPad T520 so I performed a simple check how it stays against Fedora 17 regarding power consumption. The check was very simple, only 4 tests were run on default installation of Fedora 17/18:

1. Active idle test - crond disabled and 30 min in the idle for stabilization then for 3 x 20 min the energy consumption was measured. From these 3 results the average power consumption was calculated.
2. Archive (tar.bz2) unpack - the test archive was unpack 3 times on ext4 root partition. Between each run the VM cache was dropped. Energy consumption was measured and average power consumption was calculated.
3. Kernel rebuild - kernel-3.7.4-104 srpm was rebuild in mock (one time only). Energy consumption was measured and average power consumption was calculated. In the measurement the mock setup and builddeps installation wasn't counted.
4. PowerTOP statistics (number of wakeups) - PowerTOP tool was run for 3 x 20 seconds and average number of wakeups was calculated.

For the measurement the Chroma 66202 Energy Star measurements compliant wattmeter was used. The energy consumed from the AC outlet was measured. It means that losses on the cabling and AC/DC adapter are counted in the results, so if you run on the battery the real power consumption will be slightly lower. The Lenovo ThinkPad T520 was used for the test. It has Intel Core i7-2640M CPU @ 2.80GHz and 8GB RAM. LCD backlight and wireless was turned off during the test.

Table 1: Results

Test	Fedora 17	Fedora 18
Active idle Pavg [W]	10.221	8.748
Archive unpack Pavg [W]	31.346	31.341
Kernel rebuild Pavg [W]	34.907	34.588
Wakeups count [1]	39.3	56.7

From the table 1 it is apparent that the power consumption under the load is nearly the same (probably the same due to measurement error). For the active idle the power consumption of Fedora 18 was lower. Unfortunately I haven't time to observe the reason of this, but I am going to do more tests on different HW to proof that it wasn't some anomaly. The wakeups count are comparable. Different PowerTOP versions was used for the measurement and it may be the source of the small difference. The good message is that there wasn't observed any regression in Fedora 18 regarding power consumption (on T520).