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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


    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


    I got two A8 and one A9
    A8: i.MX515(800MHz, 256KB L2) S5PC110(1GHz, 256KB L2)
    A9: AML8726-M(800MHz, 128KB L2)

    Here is the results on three platforms:
    i.MX515     S5PC110     AML8726-M
    135ms     108ms      117ms    ARM-C-CODE
    76ms   60ms      48ms    NEON-C-CODE
    17ms     13ms      20ms    NEON-ASM-CODE

    So, A9 is not the fastest.
Reply
  • Note: This was originally posted on 26th July 2011 at http://forums.arm.com


    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


    I got two A8 and one A9
    A8: i.MX515(800MHz, 256KB L2) S5PC110(1GHz, 256KB L2)
    A9: AML8726-M(800MHz, 128KB L2)

    Here is the results on three platforms:
    i.MX515     S5PC110     AML8726-M
    135ms     108ms      117ms    ARM-C-CODE
    76ms   60ms      48ms    NEON-C-CODE
    17ms     13ms      20ms    NEON-ASM-CODE

    So, A9 is not the fastest.
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