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8-42 Vol. 3
MULTIPLE-PROCESSOR MANAGEMENT
8.7.7 Performance Monitoring Counters
Performance counters and their companion control MSRs are shared between the
logical processors within a processor core for processors based on Intel NetBurst
microarchitecture. As a result, software must manage the use of these resources.
The performance counter interrupts, events, and precise event monitoring support
can be set up and allocated on a per thread (per logical processor) basis.
See Section 30.9, “Performance Monitoring and Intel Hyper-Threading Technology in
Processors Based on Intel NetBurst Microarchitecture,” for a discussion of perfor-
mance monitoring in the Intel Xeon processor MP.
In Intel Atom processor family that support Intel Hyper-Threading Technology, the
performance counters (general-purpose and fixed-function counters) and their
companion control MSRs are duplicated for each logical processor.
8.7.8 IA32_MISC_ENABLE MSR
The IA32_MISC_ENABLE MSR (MSR address 1A0H) is generally shared between the
logical processors in a processor core supporting Intel Hyper-Threading Technology.
However, some bit fields within IA32_MISC_ENABLES MSR may be duplicated per
logical processor. The partition of shared or duplicated bit fields within
IA32_MISC_ENABLES is implementation dependent. Software should program dupli
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cated fields carefully on all logical processors in the system to ensure consistent
behavior.
8.7.9 Memory Ordering
The logical processors in an Intel 64 or IA-32 processor supporting Intel Hyper-
Threading Technology obey the same rules for memory ordering as Intel 64 or IA-32
processors without Intel HT Technology (see Section 8.2, “Memory Ordering”). Each
logical processor uses a processor-ordered memory model that can be further
defined as “write-ordered with store buffer forwarding.” All mechanisms for strength
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ening or weakening the memory-ordering model to handle special programming situ-
ations apply to each logical processor.
8.7.10 Serializing Instructions
As a general rule, when a logical processor in a processor supporting Intel Hyper-
Threading Technology executes a serializing instruction, only that logical processor is
affected by the operation. An exception to this rule is the execution of the WBINVD,
INVD, and WRMSR instructions; and the MOV CR instruction when the state of the CD
flag in control register CR0 is modified. Here, both logical processors are serialized.