Intel E5-4600, CM8062101038606 Core C3 State, Core C6 State, Core C7 State, State Auto-Demotion

Power Management

A System Management Interrupt (SMI) handler returns execution to either Normal state or the C1/C1E state. See the Intel® 64 and IA-32 Architectures Software Developer’s Manual (SDM) Volumes 1, 2, and 3 for more information.

While a core is in C1/C1E state, it processes bus snoops and snoops from other threads. For more information on C1E, see Section 4.2.5.2, “Package C1/C1E”.

4.2.4.3Core C3 State

Individual threads of a core can enter the C3 state by initiating a P_LVL2 I/O read to the P_BLK or an MWAIT(C3) instruction. A core in C3 state flushes the contents of its L1 instruction cache, L1 data cache, and L2 cache to the shared L3 cache, while maintaining its architectural state. All core clocks are stopped at this point. Because the core’s caches are flushed, the processor does not wake any core that is in the C3 state when either a snoop is detected or when another core accesses cacheable memory.

4.2.4.4Core C6 State

Individual threads of a core can enter the C6 state by initiating a P_LVL3 I/O read or an MWAIT(C6) instruction. Before entering core C6, the core will save its architectural state to a dedicated SRAM. Once complete, a core will have its voltage reduced to zero volts. In addition to flushing core caches core architecture state is saved to the uncore. Once the core state save is completed, core voltage is reduced to zero. During exit, the core is powered on and its architectural state is restored.

4.2.4.5Core C7 State

Individual threads of a core can enter the C7 state by initiating a P_LVL4 I/O read to the P_BLK or by an MWAIT(C7) instruction. Core C7 and core C7 substate are the same as Core C6. The processor does not support LLC flush under any condition.

4.2.4.6C-State Auto-Demotion

In general, deeper C-states such as C6 or C7 have long latencies and have higher energy entry/exit costs. The resulting performance and energy penalties become significant when the entry/exit frequency of a deeper C-state is high. In order to increase residency in deeper C-states, the processor supports C-state auto-demotion.

There are two C-State auto-demotion options:

•C6/C7 to C3

•C3/C6/C7 To C1

The decision to demote a core from C6/C7 to C3 or C3/C6/C7 to C1 is based on each core’s immediate residency history. Upon each core C6/C7 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 or C7. 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. See the Intel® 64 and IA-32 Architectures Software Developer’s Manual (SDM) Volumes 1, 2, and 3 for C-state configurations.

Intel® Xeon® Processor E5-1600/E5-2600/E5-4600 Product Families	93
Datasheet Volume One