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Cortex-A9 : NEON assembly code is not giving expected performance compared with ARM assembly code

Mohamed Jauhar
Note: This was originally posted on 27th November 2012 at http://forums.arm.com

I am facing one problem, like I have handmade ARM9 assembly code and NEON assembly code. I expected NEON assembly should get 4X % improvement for the speed compared with ARM assembly code. But I could not see that improvement in NEON assembly code.

Can you please explain me what could be the reason?

I am using Cortex-A9 processor and configuration in my Makefile : "CFLAGS=--cpu=Cortex-A9 -O2 -Otime --apcs=/fpic --no_hide_all"

Please let me know is there anything I need to change the make file settings to get NEON performance improvement?
Parents
  • Note: This was originally posted on 22nd March 2013 at http://forums.arm.com

    Hi,

      So enabling NEON alone is not helping for me.
      As per my knowledge,NEON will not work on S registers; It will work on only Q and D registers.
      I have to get some sort of speed difference between normal ARM assembly code and NEON code right?
      My query is why I am not getting any speed difference? I should get advantage on using NEON instructions. Why It is not happening?
      I understand the memory bottleneck. But some percentage of performance gain should be there.

      Correct me If I am wrong.

    Thanks and Regards,
    KP
Reply
  • Note: This was originally posted on 22nd March 2013 at http://forums.arm.com

    Hi,

      So enabling NEON alone is not helping for me.
      As per my knowledge,NEON will not work on S registers; It will work on only Q and D registers.
      I have to get some sort of speed difference between normal ARM assembly code and NEON code right?
      My query is why I am not getting any speed difference? I should get advantage on using NEON instructions. Why It is not happening?
      I understand the memory bottleneck. But some percentage of performance gain should be there.

      Correct me If I am wrong.

    Thanks and Regards,
    KP
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