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Add AArch64 ARM Neon code (complements #1823) #1881

merged 4 commits into from May 14, 2017


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commented May 13, 2017

Pull request #1823 added AArch32 ARM Neon versions of the Blend() and Delta() functions, which are used by zoneminder's motion detection.
This pull requests complements pull request #1823 by adding AArch64 ARM Neon versions of the same functions, so both AArch32 and AArch64 are now available.
This pull request also includes a minor change to the AArch32 neon functions: relocate the data prefetches to be after the loads, to better utilize memory bus bandwidth.

In AArch64 mode, Neon is a mandatory feature of ARMv8-A CPUs, so no compiler flags are needed and no runtime detection is is needed. Neon is assumed to be always available.
Performance is pretty much identical to the AArch32 versions, but a comparison is provided:

Odroid C2 with ARM Cortex A53 processor @ 1.5 GHz:

Function Std 32bit (-O2) Std 64bit (-O2) Neon (AArch32) Neon (AArch64)
8bit Delta 215 MPixels/sec 258 MPixels/sec 968 MPixels/sec 968 MPixels/sec
32bit Delta 67 MPixels/sec 79 MPixels/sec 309 MPixels/sec 309 MPixels/sec
Fastblend 188 MColors/sec 188 MColors/sec 1130 MColors/sec 1130 MColors/sec

Scaleway ARM64-2GB instance with 2 cores of Cavium ThunderX processor:

Function Std 64bit (-O2) Neon (AArch64)
8bit Delta 174 MPixels/sec 2176 MPixels/sec
32bit Delta 68 MPixels/sec 373 MPixels/sec
Fastblend 177 MColors/sec 1757 MColors/sec

It seems the ThunderX loves Neon, or isn't as memory bound as the Cortex A53 is.

The CPU reduction should be between 20-50%. Perhaps in the future i will work on creating ARM Neon version of AlarmedPixels, which is currently the biggest CPU consumer in zma.

@knight-of-ni knight-of-ni merged commit 1e45146 into ZoneMinder:master May 14, 2017

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continuous-integration/travis-ci/pr The Travis CI build passed

@mastertheknife mastertheknife deleted the mastertheknife:aarch64_neon branch May 17, 2017

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