HT and the Thermal Monitor Feature

Refer to “The Thermal Monitoring Facilities” on page 1340 for a complete description of the Thermal Monitor feature.

In an HT-capable processor, the logical processors share the catastrophic shutdown detector and the automatic thermal monitoring mechanism.

• If the processor's core temperature rises above the catastrophic trip point, both logical processors stop execution.

• If the processor's core temperature rises above the preset automatic thermal monitor trip point, the core clock speed is modulated, affecting the execution speed of both logical processors.

Each logical processor implements its own IA32_THERM_CONTROL MSR, so software-controlled clock modulation can be enabled or disabled by either thread. This feature should either be enabled or disabled on both logical processors and, if it's enabled, the modulation duty cycle must be set to the same value on each logical processor. If the duty cycle differs, the processor clock is modulated at the lowest duty cycle selected.