XCHG (R64, R64) - Latency

Experiment 1

• Instruction: XCHG R8, R9
• Chain instructions: MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D
• Chain latency: 7
• Code:

     0:	4d 87 c8             	xchg   r8,r9
     3:	4d 63 c0             	movsxd r8,r8d
     6:	4d 63 c0             	movsxd r8,r8d
     9:	4d 63 c0             	movsxd r8,r8d
     c:	4d 63 c0             	movsxd r8,r8d
     f:	4d 63 c0             	movsxd r8,r8d
    12:	4d 63 c0             	movsxd r8,r8d
    15:	4d 63 c0             	movsxd r8,r8d
  

• Show nanoBench command
• Results:
  • Instructions retired: 8.0
  • Core cycles: 6.21
  • Reference cycles: 6.2
  • RS_UOPS_DISPATCHED: 10.0

Experiment 2

• Instruction: XCHG R8, R9
• Code:

     0:	4d 87 c8             	xchg   r8,r9
  

• Show nanoBench command
• Results:
  • Instructions retired: 1.0
  • Core cycles: 2.25
  • Reference cycles: 2.33
  • RS_UOPS_DISPATCHED: 3.0

Experiment 3 (with dependency-breaking instructions)

• Instruction: XCHG R8, R9
• Chain instruction: MOV R9, 0
• Code:

     0:	4d 87 c8             	xchg   r8,r9
     3:	49 c7 c1 00 00 00 00 	mov    r9,0x0
  

• Show nanoBench command
• Results:
  • Instructions retired: 2.0
  • Core cycles: 1.35
  • Reference cycles: 1.35
  • RS_UOPS_DISPATCHED: 4.0

Experiment 1

• Instruction: XCHG R8, R9
• Chain instructions: MOVSX R8, R9D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D
• Chain latency: 7
• Code:

     0:	4d 87 c8             	xchg   r8,r9
     3:	4d 63 c1             	movsxd r8,r9d
     6:	4d 63 c0             	movsxd r8,r8d
     9:	4d 63 c0             	movsxd r8,r8d
     c:	4d 63 c0             	movsxd r8,r8d
     f:	4d 63 c0             	movsxd r8,r8d
    12:	4d 63 c0             	movsxd r8,r8d
    15:	4d 63 c0             	movsxd r8,r8d
  

• Show nanoBench command
• Results:
  • Instructions retired: 8.0
  • Core cycles: 9.0
  • Reference cycles: 9.0
  • RS_UOPS_DISPATCHED: 10.0

Experiment 1

• Instruction: XCHG R9, R8
• Chain instructions: MOVSX R8, R9D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D
• Chain latency: 7
• Code:

     0:	4d 87 c1             	xchg   r9,r8
     3:	4d 63 c1             	movsxd r8,r9d
     6:	4d 63 c0             	movsxd r8,r8d
     9:	4d 63 c0             	movsxd r8,r8d
     c:	4d 63 c0             	movsxd r8,r8d
     f:	4d 63 c0             	movsxd r8,r8d
    12:	4d 63 c0             	movsxd r8,r8d
    15:	4d 63 c0             	movsxd r8,r8d
  

• Show nanoBench command
• Results:
  • Instructions retired: 8.0
  • Core cycles: 9.08
  • Reference cycles: 9.09
  • RS_UOPS_DISPATCHED: 10.0

Experiment 1

• Instruction: XCHG R9, R8
• Chain instructions: MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D;MOVSX R8, R8D
• Chain latency: 7
• Code:

     0:	4d 87 c1             	xchg   r9,r8
     3:	4d 63 c0             	movsxd r8,r8d
     6:	4d 63 c0             	movsxd r8,r8d
     9:	4d 63 c0             	movsxd r8,r8d
     c:	4d 63 c0             	movsxd r8,r8d
     f:	4d 63 c0             	movsxd r8,r8d
    12:	4d 63 c0             	movsxd r8,r8d
    15:	4d 63 c0             	movsxd r8,r8d
  

• Show nanoBench command
• Results:
  • Instructions retired: 8.0
  • Core cycles: 6.24
  • Reference cycles: 6.26
  • RS_UOPS_DISPATCHED: 10.0

Experiment 2

• Instruction: XCHG R9, R8
• Code:

     0:	4d 87 c1             	xchg   r9,r8
  

• Show nanoBench command
• Results:
  • Instructions retired: 1.0
  • Core cycles: 2.25
  • Reference cycles: 2.24
  • RS_UOPS_DISPATCHED: 3.0

Experiment 3 (with dependency-breaking instructions)

• Instruction: XCHG R9, R8
• Chain instruction: MOV R9, 0
• Code:

     0:	4d 87 c1             	xchg   r9,r8
     3:	49 c7 c1 00 00 00 00 	mov    r9,0x0
  

• Show nanoBench command
• Results:
  • Instructions retired: 2.0
  • Core cycles: 1.34
  • Reference cycles: 1.37
  • RS_UOPS_DISPATCHED: 4.0