Core C0 State; Core C1/C1E State; Core C3 State; Core C6 State - Intel BX80619I73960X Datasheet

Power Management
4.2.4.1

Core C0 State

The normal operating state of a core where code is being executed.
4.2.4.2

Core C1/C1E State

C1/C1E is a low power state entered when all threads within a core execute a HLT or
MWAIT(C1/C1E) instruction.
A System Management Interrupt (SMI) handler returns execution to either Normal
state or the C1/C1E state. See the Intel
Developer's Manual, Volume 3A/3B: System Programmer's Guide 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
4.2.4.3

Core 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.
4.2.4.4

Core 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. During exit, the core is powered on and its architectural state is restored. 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.
4.2.4.5

Core 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.
4.2.4.6

C-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. 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
• C7/C6/C3 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.
Datasheet, Volume 1
®
64 and IA-32 Architecture Software
Section 4.2.5.2, "Package C1/C1E".
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