Data Sheet

Power Management
72 Datasheet, Volume 1 of 2
4.2.1.2 Intel
®
Speed Shift Technology
Intel Speed Shift Technology is an energy efficient method of frequency control by the
hardware rather than relying on OS control. OS is aware of available hardware P-states
and request a desired P-state or it can let Hardware determine the P-state. The OS
request is based on its workload requirements and awareness of processor capabilities.
Processor decision is based on the different system constraints for example: Workload
demand, thermal limits while taking into consideration the minimum and maximum
levels and activity window of performance requested by the operating system.
For more details, refer to the following document (Refer related documents section):
Intel
®
64 and IA-32 Architectures Software Developer’s Manual (SDM), Volume 3B
4.2.2 Low-Power Idle States
When the processor is idle, low-power idle states (C-states) are used to save power.
More power savings actions are taken for numerically higher C-states. However, deeper
C-states have longer exit and entry latencies. Resolution of C-states occur at the
thread, processor IA core, and processor package level. Thread-level C-states are
available if Intel Hyper-Threading Technology is enabled.
Caution: Long term reliability cannot be assured unless all the Low-Power Idle States are
enabled.
While individual threads can request low-power C-states, power saving actions only
take place once the processor IA core C-state is resolved. processor IA core C-states
are automatically resolved by the processor. For thread and processor IA core C-states,
a transition to and from C0 state is required before entering any other C-state.
Figure 4-3. Idle Power Management Breakdown of the Processor IA Cores