acpi_task_0 consuming cpu resource

[C. C. Tang]

Hi.

I have a system with Intel D945GCLF2 motherboard with Atom CPU.
I found that when I enable auto speed regulation of case fan.
FreeBSD will have a process "acpi_task_0" which consume all resource of 
one of the core of the CPU.
The fan seems fail to change RPM itself. Is there any solution to this 
problem without disabling the auto speed regulation?

   PID USERNAME       THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU 
COMMAND
     7 root             1   8    -     0K     8K CPU1   0 124:29 100.00% 
acpi_task_0
    12 root             1 171 ki31     0K     8K RUN    0 177:23 95.26% 
idle: cpu0
    11 root             1 171 ki31     0K     8K RUN    1  61:20  1.07% 
idle: cpu1

Thanks very much.
C.C.