Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

7-26 Vol. 3A

MULTIPLE-PROCESSOR MANAGEMENT

7.7.3 Executing Multiple Threads on an Intel

64 or IA-32

Processor Supporting Hardware Multi-Threading

Upon completing the operating system boot-up procedure, the bootstrap processor

(BSP) executes operating system code. Other logical processors are placed in the

halt state. To execute a code stream (thread) on a halted logical processor, the oper-

ating system issues an interprocessor interrupt (IPI) addressed to the halted logical

processor. In response to the IPI, the processor wakes up and begins executing the

thread identified by the interrupt vector received as part of the IPI.

To manage execution of multiple threads on logical processors, an operating system

can use conventional symmetric multiprocessing (SMP) techniques. For example, the

operating-system can use a time-slice or load balancing mechanism to periodically

interrupt each of the active logical processors. Upon interrupting a logical processor,

the operating system checks its run queue for a thread waiting to be executed and

dispatches the thread to the interrupted logical processor.

7.7. 4 H a nd lin g Int errupt s on an IA-32 Processor Supporting

Hardware Multi-Threading

Interrupts are handled on processors supporting Hyper-Threading Technology as

they are on conventional MP systems. External interrupts are received by the I/O

APIC, which distributes them as interrupt messages to specific logical processors

(see Figure 7-3).

Logical processors can also send IPIs to other logical processors by writing to the ICR

also applies to dual-core processors.