19-140 Vol. 3B

PERFORMANCE-MONITORING EVENTS

D2H

02H

RAT_STALLS.

PARTIAL_CYCLES

Partial register stall 

cycles.

This event counts the number of cycles instruction 

execution latency became longer than the defined latency 

because the instruction uses a register that was partially 

written by previous instructions. 

D2H

04H

RAT_STALLS.

FLAGS

Flag stall cycles.

This event counts the number of cycles during which 

execution stalled due to several reasons, one of which is a 

partial flag register stall. 
A partial register stall may occur when two conditions are 

met: 
• An instruction modifies some, but not all, of the flags in 

the flag register.

• The next instruction, which depends on flags, depends on 

flags that were not modified by this instruction.

D2H

08H

RAT_STALLS.

FPSW

FPU status word stall. This event indicates that the FPU status word (FPSW) is 

written. To obtain the number of times the FPSW is written 

divide the event count by 2.
The FPSW is written by instructions with long latency; a 

small count may indicate a high penalty.

D2H

0FH

RAT_STALLS.

ANY

All RAT stall cycles.

This event counts the number of stall cycles due to 

conditions described by: 
• RAT_STALLS.ROB_READ_PORT

• RAT_STALLS.PARTIAL

• RAT_STALLS.FLAGS

• RAT_STALLS.FPSW.

D4H

01H

SEG_RENAME_

STALLS.ES

Segment rename stalls 

- ES.

This event counts the number of stalls due to the lack of 

renaming resources for the ES segment register. If a 

segment is renamed, but not retired and a second update to 

the same segment occurs, a stall occurs in the front end of 

the pipeline until the renamed segment retires. 

D4H

02H

SEG_RENAME_

STALLS.DS

Segment rename stalls 

- DS.

This event counts the number of stalls due to the lack of 

renaming resources for the DS segment register. If a 

segment is renamed, but not retired and a second update to 

the same segment occurs, a stall occurs in the front end of 

the pipeline until the renamed segment retires. 

D4H

04H

SEG_RENAME_

STALLS.FS

Segment rename stalls 

- FS.

This event counts the number of stalls due to the lack of 

renaming resources for the FS segment register. 
If a segment is renamed, but not retired and a second 

update to the same segment occurs, a stall occurs in the 

front end of the pipeline until the renamed segment retires. 

D4H

08H

SEG_RENAME_

STALLS.GS

Segment rename stalls 

- GS.

This event counts the number of stalls due to the lack of 

renaming resources for the GS segment register. 
If a segment is renamed, but not retired and a second 

update to the same segment occurs, a stall occurs in the 

front end of the pipeline until the renamed segment retires. 

D4H

0FH

SEG_RENAME_

STALLS.ANY

Any (ES/DS/FS/GS) 

segment rename stall.

This event counts the number of stalls due to the lack of 

renaming resources for the ES, DS, FS, and GS segment 

registers.
If a segment is renamed but not retired and a second update 

to the same segment occurs, a stall occurs in the front end 

of the pipeline until the renamed segment retires. 

Table 19-23.  Non-Architectural Performance Events in Processors Based on Intel® Core™ Microarchitecture (Contd.)

Event 

Num

Umask

Value

Event Name 

Definition

Description and

Comment