Intel i5-2500K BX80623I52500K User Manual

Datasheet, Volume 1

49

Power Management

There are two C-State auto-demotion options:

• C6  to  C3
• C6/C3 To C1

The decision to demote a core from C6 to C3 or C3/C6 to C1 is based on each core’s 
immediate residency history. Upon each core C6 request, the core C-state is demoted 
to C3 or C1 until a sufficient amount of residency has been established. At that point, a 
core is allowed to go into C3/C6. Each option can be run concurrently or individually.

This feature is disabled by default. BIOS must enable it in the 
PMG_CST_CONFIG_CONTROL register. The auto-demotion policy is also configured by 
this register. 

The processor supports C0, C1/C1E, C3, and C6 power states. The following is a 
summary of the general rules for package C-state entry. These apply to all package C-
states unless specified otherwise:

• A package C-state request is determined by the lowest numerical core C-state 

amongst all cores.

• A package C-state is automatically resolved by the processor depending on the 

core idle power states and the status of the platform components.

— Each core can be at a lower idle power state than the package if the platform 

does not grant the processor permission to enter a requested package C-state.

— The platform may allow additional power savings to be realized in the 

processor.

— For package C-states, the processor is not required to enter C0 before entering 

any other C-state.

The processor exits a package C-state when a break event is detected. Depending on 
the type of break event, the processor does the following:

• If a core break event is received, the target core is activated and the break event 

message is forwarded to the target core.

— If the break event is not masked, the target core enters the core C0 state and 

the processor enters package C0.

• If the break event was due to a memory access or snoop request.

— But the platform did not request to keep the processor in a higher package C-

state, the package returns to its previous C-state.

— And the platform requests a higher power C-state, the memory access or snoop 

request is serviced and the package remains in the higher power C-state.