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The processor supports C0, C2, C3, C6, C8, and C10 package 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 processor IA core C-state amongst all processor IA cores.
- A package C-state is automatically resolved by the processor depending on the processor IA core idle power states and the status of the platform components.
- Each processor IA 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.
- Entry into a package C-state may be subject to auto-demotion – that is, the processor may keep the package in a deeper package C-state then requested by the operating system if the processor determines, using heuristics, that the deeper C-state results in better power/performance.
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 processor IA core break event is received, the target processor IA core is activated and the break event message is forwarded to the target processor IA core.
- If the break event was due to a memory access or snoop request,
PKG C2 and C3 can not be requested explicitly by the software
Package C-State Auto-Demotion
The Processor may demote the Package C state to a shallower C state, for example instead of going into package C10, it will demote to package C8 (and so on as required). The processor decision to demote the package C state is based on the required C states latencies, entry/exit energy/power and devices LTR.
Modern Standby is a platform state. On display time out the OS requests the processor to enter package C10 and platform devices at RTD3 (or disabled) in order to attain low power in idle. Modern Standby requires proper BIOS and OS configuration.
Dynamic LLC Sizing
When all processor IA cores request C8 or deeper C-state, internal heuristics dynamically flushes the LLC. Once the processor IA cores enter a deep C-state, depending on their MWAIT sub-state request, the LLC is either gradually flushed N-ways at a time or flushed all at once. Upon the processor IA cores exiting to C0 state, the LLC is gradually expanded based on internal heuristics.