[ltp] Deep CPU Cx states

[Laurent Gilson]

Hello,

>> Look at /proc/acpi/processor/CPU/power. Does the bus master activity  
>> drop
>> to 000...000 if you do nothing ? Do the cores reach C4 or deeper ?
>
> I have never seen anything reach deeper than C4 on Linux ACPI... you  
> need to tell the kernel to allow it, I suppose?

You need to have a very limited board (or no drivers loaded). These  
http://www.commell.com.tw/Product/COM%20Express/CES-470.htm reach C6.

The kernel just tries to prevent data loss. As soon as another bus master  
beside the CPU is detected all lower states are blocked. Which is a GOOD  
THING (tm). Cache corruption is nearly impossible to fix and very hard to  
debug. On laptops C4, maybe C5 is the best you can expect.

cu