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24332E—December 2002
20
Processor Performance Counters Do Not Count Some x86 Instructions
Products Affected. A0, A2, A5
Normal Specified Operation. The processor should count all x86 instructions when programmed to do so.
Non-conformance. There are two types of uncounted instructions. One set of instructions is always
uncounted. Another set of instructions are uncounted only if a certain data dependency exists.
Instructions never counted are: RDMSR, WRMSR, FSTENV, FSAVE, FLDENV, FPTAN, FYL2XP1,
FCLEX, LLDT, LTR, MOV CRx, LGDT, LIDT, INVLPG, INVD, WBINVD, MOV DRx, CPUID, and
SFENCE.
Instructions that are uncounted only when certain data dependencies exist are:
■
LAR, LSL, VERR, VERW if they clear the Zero Flag
■
FXSAVE, FXRSTOR if FERR is changed
■
FPU instructions with exceptional data conditions
■
IO instructions that detect an interrupt
■
POPF with the trap flag =1
■
POPFD and PUSHFD with IOPL not equal 3 and Virtual Mode enabled
■
POPFD when Alignment Check is being enabled
■
MOV SS with the trap flag =1
■
Segment Loads that generate accessed bit exceptions
■
STI with the trap flag or the interrupt flag already a 1
■
CLTS with the CR0.TS flag =1
■
LMSW that changes any bit
Potential Effect on System. Performance counter may under count the actual number of x86 instructions.
Suggested Workaround. Versions of the AMD Athlon™ processor not affected by this erratum may be used
to gather instruction counts.
Resolution Status. No fix planned.
Preliminary Information
AMD Athlon™ Processor Model 6 Revision Guide
11
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