14-10 Vol. 3B
POWER AND THERMAL MANAGEMENT
The IA32_MPERF MSR and IA32_APERF MSR mechanism (see Section 14.2) allows the OS to calculate the resultant
effective frequency delivered over a time period. Energy efficiency and performance optimizations directly impact
the resultant effective frequency delivered.
The layout of the IA32_HWP_STATUS MSR is shown in Figure 14-8. It provides feedback regarding changes to
IA32_HWP_CAPABILITIES.Guaranteed_Performance and excursions to
IA32_HWP_CAPABILITIES.Minimum_Performance. The bit fields are described below:
•
Guaranteed_Performance_Change (bit 0, RWC0) — If set (1), a change to Guaranteed_Performance has
occurred. Software should query IA32_HWP_CAPABILITIES.Guaranteed_Performance value to ascertain the
new Guaranteed Performance value and to assess whether to re-adjust HWP hints via IA32_HWP_REQUEST.
Software must clear this bit by writing a zero (0).
•
Excursion_To_Minimum (bit 2, RWC0) — If set (1), an excursion to Minimum_Performance of
IA32_HWP_REQUEST has occurred. Software must clear this bit by writing a zero (0).
•
Bits 63:3, and bit 1 are reserved and must be zero.
The status bits of IA32_HWP_STATUS must be cleared (0) by software so that a new status condition change will
cause the hardware to set the bit again and issue the notification. Status bits are not set for “normal” excursions
e.g. running below Minimum Performance for short durations during C-state exit. Changes to
Guaranteed_Performance and excursions to Minimum_Performance will occur no more than once per second.
The OS can determine the specific reasons for a Guaranteed_Performance change or an excursion to
Minimum_Performance in IA32_HWP_REQUEST by examining the associated status and log bits reported in the
IA32_THERM_STATUS MSR. The layout of the IA32_HWP_STATUS MSR that HWP uses to support software query of
HWP feedback is shown in Figure 14-9. The bit fields of IA32_THERM_STATUS associated with HWP feedback are
described below (Bit fields of IA32_THERM_STATUS unrelated to HWP can be found in Section 14.7.5.2).
Figure 14-8. IA32_HWP_STATUS MSR
Figure 14-9. IA32_THERM_STATUS Register With HWP Feedback
63
0
Reserved
1
Excursion_To_Minimum
2
3
Reserved
Guaranteed_Performance_Change
63
0
Reserved
15
Reading Valid
1
2
3
4
5
8
10
16
22
23
27
Resolution in Deg. Celsius
Digital Readout
Thermal Threshold #2 Log
Thermal Threshold #2 Status
Thermal Threshold #1 Log
Thermal Threshold #1 Status
Critical Temperature Log
6
7
9
31
32
Critical Temperature Status
PROCHOT# or FORCEPR# Log
PROCHOT# or FORCEPR# Event
Thermal Status Log
Thermal Status
11
Power Limit Notification Log
Power Limit Notification Status
14 13 12
Cross-domain Limit Log
Cross-domain Limit Status
Current Limit Log
Current Limit Status