
32
Dual-Core Intel Xeon Processor 5100 Series Specification Update
AG65.
Performance Monitoring Event FP_ASSIST May Not be Accurate
Problem:
Performance monitoring event FP_ASSIST (11H) may be inaccurate as assist events
may 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
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.
AG66.
CPL-Qualified BTS May Report Incorrect Branch-From Instruction
Record From Address
Problem:
CPL (Current Privilege Level)-qualified BTS (Branch Trace Store) may report incorrect
branch-from instruction record From address under the following conditions:
Either BTS_OFF_OS[9] or BTS_OFF_USR[10] is selected in IA32_DEBUGCTL 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.
AG67.
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.
Do not use performance monitoring counters for precise event sampling when the
precise event is dependent on the CPL value.
Workaround: None identified.
Status:
For the steppings affected, see the Summary Tables of Changes.
AG68.
PMI May be Delayed to Next PEBS Event
Problem:
After a PEBS (Precise Event-Based Sampling) event, the PEBS index is compared with
the PEBS threshold, and the index is incremented with every event. If PEBS index is
equal to the PEBS threshold, a PMI (Performance Monitoring Interrupt) should be
issued. Due to this erratum, the PMI may be delayed by one PEBS event.
Implication: Debug Store Interrupt Service Routines may observe delay of PMI occurrence by one
PEBS event.
Workaround: None identified.
Status:
For the steppings affected, see the Summary Tables of Changes.
Problem:
exiting CC3/CC4 low power states and continuing program execution.
Implication: When this erratum occurs, the processor may livelock, resulting in a system hang.
Workaround: It is possible for the BIOS to contain a workaround for this erratum.