• Locked Locked
  • Replies 3 replies
  • Subscribers 119 subscribers
  • Views 2929 views
  • Users 0 members are here
2025 survey

We are running a survey to help us improve the experience for all of our members. If you see the survey appear, please take the time to tell us about your experience if you can.

Options
Related
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Cortex-R4F : need explanations about some PMU events

Christophe Beausoleil
Note: This was originally posted on 29th July 2011 at http://forums.arm.com

Hello,

I am using a Cortex-R4F (TMS570), and I used PMU to count the number of "Instruction architecturally executed" and "Dual-issued pair of instructions architecturally executed" (§6.1 of DDI0363E) in order to benchmark that component, and I get a strange result : I built a test code with 4096 instructions (in fact, a little bit more before and after the PMU is started/stopped), and I obtained :
- in ARM mode :
     3083 Instruction architecturally executed
     2048 Dual-issued pair of instructions architecturally executed

- in Thumb mode :
     4015 Instruction architecturally executed
     2048 Dual-issued pair of instructions architecturally executed

Please, could someone explain why the number of Instruction architecturally executed is not the same in both modes ?
And more important for me : how can I count the real number of instructions of any code ?

Thanks a lot

Best regards

Christophe
Parents
  • Arm Employee Badge
    Note: This was originally posted on 20th February 2012 at http://forums.arm.com

    You said that it should be 4096, how do you know this? What are you writing the code in?  C will typically compile to more Thumb instructions than ARM instructions*, so what you've seen isn't necessarily wrong.

    * There are cases where ARM instructions are more flexible than Thumb instructions.  So the compiler can use one ARM instr or two Thumb instrs.  This is less common with Thumb-2, but there are still some instances.
Reply
  • Arm Employee Badge
    Note: This was originally posted on 20th February 2012 at http://forums.arm.com

    You said that it should be 4096, how do you know this? What are you writing the code in?  C will typically compile to more Thumb instructions than ARM instructions*, so what you've seen isn't necessarily wrong.

    * There are cases where ARM instructions are more flexible than Thumb instructions.  So the compiler can use one ARM instr or two Thumb instrs.  This is less common with Thumb-2, but there are still some instances.
Children
No data