
Power
Note: When P_LVLx I/O instructions are used, MWAIT
4.2.4Core C-State Rules
The following are general rules for all core
•A core
•A core transitions to C0 state when:
—An interrupt occurs
—There is an access to the monitored address if the state was entered using an MWAIT/Timed MWAIT instruction
—The deadline corresponding to the Timed MWAIT instruction expires
•An interrupt directed toward a single thread wakes only that thread.
•If any thread in a core is in active (in C0 state), the core's
•Any interrupt coming into the processor package may wake any core.
•A system reset
Core C0 State
The normal operating state of a core where code is being executed.
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® 64 and
While a core is in C1/C1E state, it processes bus snoops and snoops from other threads. For more information on C1E state, see Package
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.
| Intel® Xeon® Processor |
June 2013 | Datasheet – Volume 1 of 2 |
Order No.: | 53 |