Datasheet

Errata

68 Specification Update

AH67. Performance Monitoring Event FP_ASSIST May Not Be Accurate

Problem: Performance monitoring event FP_ASSIST (11H) may be inaccurate as assist events

will be counted twice per actual assist in the following specific cases:

 FADD and FMUL instructions with a NaN(Not a Number) operand and a memory

operand

 FDIV instruction with zero operand value in memory

Problem: In addition, an assist event may be counted when DAZ (Denormals-Are-Zeros) and

FTZ (Flush-To-Zero) flags are turned on even though no actual assist occurs.

Implication: The counter value for the performance monitoring event FP_ASSIST (11H) may be

larger than expected. The size of the error is dependent on the number of occurrences

of the above conditions while the event is active.

Workaround: None identified.

Status: For the steppings affected, see the Summary Tables of Changes.

AH68. CPL-Qualified BTS May Report Incorrect Branch-From Instruction

Address

Problem: CPL (Current Privilege Level)-qualified BTS (Branch Trace Store) may report incorrect

branch-from instruction address under the following conditions:

 Either BTS_OFF_OS [9] or BTS_OFF_USR [10] is selected in IA32_DEBUGCTLC

MSR (1D9H).

 Privilege-level transitions occur between CPL > 0 and CPL 0 or vice versa.

Implication: Due to this erratum, the From address reported by BTS may be incorrect for the

described conditions.

Workaround: None Identified

Status: For the steppings affected, see the Summary Tables of Changes.

AH69. PEBS Does Not Always Differentiate Between CPL-Qualified Events

Problem: Performance monitoring counter configured to sample PEBS (Precise Event Based

Sampling) events at a certain privilege level may count samples at the wrong privilege

level.

Implication: Performance monitoring counter may be higher than expected for CPL-qualified

events.

Workaround: Do not use performance monitoring counters for precise event sampling when the

precise event is dependent on the CPL value.

Status: For the steppings affected, see the Summary Tables of Changes.