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Differences between NEON in Cortex-A8 and A9

Kun Feng
Note: This was originally posted on 25th July 2011 at http://forums.arm.com

Currently i am working on a Cortex-A9 single-core chip(AML8726-m if you want to know more), and in the datasheet it's said there is a neon in it. But when i test the code here(http://hilbert-space.de/?p=22), i cannot find any acceleration on it, sometimes the neon-assembly- optimized code runs even slower than the arm-c-code. At the same time, the same code can get a pretty good acceleration on my i.MX515 which is a Cortex-A8 chip.


I am using the Android NDK to build a test app running on Android, can it be the reason?
Can anyone tell me why it happens? 


Here is some results:
#####On A8#####
arm c code: 116.*** ms
neon c code: 83.*** ms
neon asm code: 51.*** ms
#####On A9#####
arm c code: 107.*** ms
neon c code: 106-107.*** ms
neon asm code: 106-107.*** ms

Android is Linux based OS, so I can call gettimeofday() to get a precise time period in us level. The results on A9 are not identical but almost the same and I didn't run the same binary 3 times, I'm sure.

Thanks and looking forward to any useful suggestions.


Parents
  • Note: This was originally posted on 26th July 2011 at http://forums.arm.com


    Thank you so much!!!
    You are right, when I changed the image size from 10MB to 50KB, I got the wanted time----about 5-6 times faster
    I didn't know the memory access is so time consuming before.
    I can move forward now, thanks again.


    Ok.

    and finaly :
    Does the cortex A9 faster than the cortex A8 ?

    Can you give your result (c / asm / neon) for the both proc with the small picture ?
    Can you give the freqency of your proc too ?

    thank's
Reply
  • Note: This was originally posted on 26th July 2011 at http://forums.arm.com


    Thank you so much!!!
    You are right, when I changed the image size from 10MB to 50KB, I got the wanted time----about 5-6 times faster
    I didn't know the memory access is so time consuming before.
    I can move forward now, thanks again.


    Ok.

    and finaly :
    Does the cortex A9 faster than the cortex A8 ?

    Can you give your result (c / asm / neon) for the both proc with the small picture ?
    Can you give the freqency of your proc too ?

    thank's
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