Intel BX80646E31230V3, BX80646E31240V3 4.2.2Low-PowerIdle States

Power Management—Processor

•Multiple frequency and voltage points for optimal performance and power efficiency. These operating points are known as P-states.

•Frequency selection is software controlled by writing to processor MSRs. The voltage is optimized based on the selected frequency and the number of active processor cores.

—Once the voltage is established, the PLL locks on to the target frequency.

—All active processor cores share the same frequency and voltage. In a multi- core processor, the highest frequency P-state requested among all active cores is selected.

—Software-requested transitions are accepted at any time. If a previous transition is in progress, the new transition is deferred until the previous transition is completed.

•The processor controls voltage ramp rates internally to ensure glitch-free transitions.

•Because there is low transition latency between P-states, a significant number of transitions per-second are possible.

4.2.2Low-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, higher C-states have longer exit and entry latencies. Resolution of C-states occur at the thread, processor 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.

Figure 12. Idle Power Management Breakdown of the Processor Cores

Thread 0 Thread 1 Thread 0 Thread 1

Core 0 State Core N State

Processor Package State

Entry and exit of the C-states at the thread and core level are shown in the following figure.

	Intel® Xeon® Processor E3-1200 v3 Product Family
June 2013	Datasheet – Volume 1 of 2
Order No.: 328907-001	51