• Locked Locked
  • Replies 5 replies
  • Subscribers 119 subscribers
  • Views 4398 views
  • Users 0 members are here
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

Neon reg to ARM reg data transfer

Vishwa Vishwa
Note: This was originally posted on 30th July 2009 at http://forums.arm.com

I m transferring data from neon register to arm register, which is very costly.
i.e., it takes each vmov.32 r6,do[2] takes around 13 to 18 cycles.
This is proving to be very costly for a function which runs for many times.

Can anyone please suggest a way out of this???

Thanks in advance for any help..... :)
Parents
  • Arm Employee Badge
    Note: This was originally posted on 30th July 2009 at http://forums.arm.com

    You cannot reduce the NEON-ARM or ARM-NEON register move costs - these are caused by the microarchitecture of the NEON unit for the Cortex-A8.

    One of the key parts of vectorizing for the Neon unit is to try and minimize the interaction between the main ARM pipeline and the NEON unit - pushing relatively large blocks of code through the NEON without too much dependence on what is happening on the ARM-pipeline. Any interaction is fairly time consuming as you have noted, but for many common tasks such a media CODECs the need for interaction is actually quite low.

    It is worth noting that the NEON unit has its own load store hardware so the NEON code can make its own memory accesses, and does *not* need the ARM to load data for it (this then has to be vmov'd in to the NEON which is slow).
Reply
  • Arm Employee Badge
    Note: This was originally posted on 30th July 2009 at http://forums.arm.com

    You cannot reduce the NEON-ARM or ARM-NEON register move costs - these are caused by the microarchitecture of the NEON unit for the Cortex-A8.

    One of the key parts of vectorizing for the Neon unit is to try and minimize the interaction between the main ARM pipeline and the NEON unit - pushing relatively large blocks of code through the NEON without too much dependence on what is happening on the ARM-pipeline. Any interaction is fairly time consuming as you have noted, but for many common tasks such a media CODECs the need for interaction is actually quite low.

    It is worth noting that the NEON unit has its own load store hardware so the NEON code can make its own memory accesses, and does *not* need the ARM to load data for it (this then has to be vmov'd in to the NEON which is slow).
Children
No data