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

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?

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Shervin Emami over 12 years ago

Note: This was originally posted on 22nd March 2013 at http://forums.arm.com

Like I said, the multiplication hardware is only 32-bits wide, so multiplying Q registers is roughly the same speed as multiplying S registers 4 times, as mentioned in the cycle timing of the Cortex-A9 NEON TRM.
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Shervin Emami over 12 years ago

Note: This was originally posted on 22nd March 2013 at http://forums.arm.com

Like I said, the multiplication hardware is only 32-bits wide, so multiplying Q registers is roughly the same speed as multiplying S registers 4 times, as mentioned in the cycle timing of the Cortex-A9 NEON TRM.
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