Intel_pstate: One Core always 100% C0 state and never scale down

[Light <sgsdxzy@gmail.com>]

I am using a laptop with Intel Ivy bridge core i7 3610QM. I updated my 
kernel to 3.10 and started to use intel_pstate as scaling driver:
#cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_driver
intel_pstate

However I find that one of my four cores is always in C0 state even when 
there is no activities. I monitored it using i7z:
Core [core-id]  :Actual Freq (Mult.)      C0%   Halt(C1)%  C3 %   C6 %   
C7 %  Temp
         Core 1 [0]:       3288.24 (32.97x)      99.7       0 0       
0       0    83
         Core 2 [1]:       3138.62 (31.47x)         1       0 0       
0    99.7    74
         Core 3 [2]:       3175.46 (31.84x)         1    0.891 0       
0      99    76
         Core 4 [3]:       3177.34 (31.86x)         1    0.21 0       
0    99.3    71

Also cpu frequencies never scale down, resulting in very high temp.
#cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor
powersave

It does say powersave, and my cpu is capable of 1.20Ghz to 3.30Ghz

I don't know if I misconfigured or misunderstood something. Can someone 
tell me why?
Thanks!