I'm seeing the same issue on 3.18.6-1-ARCH.
[samer@archbox ~]$ sudo powertop --auto-tune
Loaded 34 prior measurements
Cannot load from file /var/cache/powertop/saved_parameters.powertop
RAPL device for cpu 0
RAPL Using PowerCap Sysfs : Domain Mask f
RAPL device for cpu 0
RAPL Using PowerCap Sysfs : Domain Mask f
RAPL device for cpu 0
RAPL Using PowerCap Sysfs : Domain Mask f
Devfreq not enabled
Cannot load from file /var/cache/powertop/saved_parameters.powertop
unknown op '{'
To show power estimates do 263 measurement(s) connected to battery
onlyLeaving PowerTOP
*** Error in `powertop': corrupted double-linked list:
0x0000000000fbceb0 ***
Any idea what's causing this?