Vol. 3A 8-31
MULTIPLE-PROCESSOR MANAGEMENT
When a logical processor performs a TLB invalidation operation, only the TLB entries that are tagged for that logical
processor are guaranteed to be flushed. This protocol applies to all TLB invalidation operations, including writes to
control registers CR3 and CR4 and uses of the INVLPG instruction.
8.7.13.3 Thermal Monitor
In a processor that supports Intel Hyper-Threading Technology, logical processors share the catastrophic shutdown
detector and the automatic thermal monitoring mechanism (see Section 14.7, “Thermal Monitoring and Protec-
tion”). Sharing results in the following behavior:
•
If the processor’s core temperature rises above the preset catastrophic shutdown temperature, the processor
core halts execution, which causes both logical processors to stop execution.
•
When the processor’s core temperature rises above the preset automatic thermal monitor trip temperature, the
frequency of the processor core is automatically modulated, which effects the execution speed of both logical
processors.
For software controlled clock modulation, each logical processor has its own IA32_CLOCK_MODULATION MSR,
allowing clock modulation to be enabled or disabled on a logical processor basis. Typically, if software controlled
clock modulation is going to be used, the feature must be enabled for all the logical processors within a physical
processor and the modulation duty cycle must be set to the same value for each logical processor. If the duty cycle
values differ between the logical processors, the processor clock will be modulated at the highest duty cycle
selected.
8.7.13.4 External Signal Compatibility
This section describes the constraints on external signals received through the pins of a processor supporting Intel
Hyper-Threading Technology and how these signals are shared between its logical processors.
•
STPCLK# — A single STPCLK# pin is provided on the physical package of the Intel Xeon processor MP. External
control logic uses this pin for power management within the system. When the STPCLK# signal is asserted, the
processor core transitions to the stop-grant state, where instruction execution is halted but the processor core
continues to respond to snoop transactions. Regardless of whether the logical processors are active or halted
when the STPCLK# signal is asserted, execution is stopped on both logical processors and neither will respond
to interrupts.
In MP systems, the STPCLK# pins on all physical processors are generally tied together. As a result this signal
affects all the logical processors within the system simultaneously.
•
LINT0 and LINT1 pins — A processor supporting Intel Hyper-Threading Technology has only one set of LINT0
and LINT1 pins, which are shared between the logical processors. When one of these pins is asserted, both
logical processors respond unless the pin has been masked in the APIC local vector tables for one or both of the
logical processors.
Typically in MP systems, the LINT0 and LINT1 pins are not used to deliver interrupts to the logical processors.
Instead all interrupts are delivered to the local processors through the I/O APIC.
•
A20M# pin — On an IA-32 processor, the A20M# pin is typically provided for compatibility with the Intel 286
processor. Asserting this pin causes bit 20 of the physical address to be masked (forced to zero) for all external
bus memory accesses. Processors supporting Intel Hyper-Threading Technology provide one A20M# pin, which
affects the operation of both logical processors within the physical processor.
The functionality of A20M# is used primarily by older operating systems and not used by modern operating
systems. On newer Intel 64 processors, A20M# may be absent.
8.8 MULTI-CORE
ARCHITECTURE
This section describes the architecture of Intel 64 and IA-32 processors supporting dual-core and quad-core tech-
nology. The discussion is applicable to the Intel Pentium processor Extreme Edition, Pentium D, Intel Core Duo,
Intel Core 2 Duo, Dual-core Intel Xeon processor, Intel Core 2 Quad processors, and quad-core Intel Xeon proces-
sors. Features vary across different microarchitectures and are detectable using CPUID.