DRdragontamer·Oct 8, 2018
I can't say I've used AVX512 personally.
But what I can say, is that AVX and AVX2 are rather limiting. And I want those new instructions that are found only in AVX512.
Not even to run 512-bit computations mind you. I want to run 128-bit computations in AVX512. You can use XMM registers in AVX512 ya know!!
The main benefits of AVX512 are the mask registers, scatter-instructions (AVX / AVX2 have gather, but no scatter), and an extension all the way to 32 XMM / YMM / ZMM registers
True, using ZMM registers causes severe downclocking issues. But XMM (128-bit) and YMM (256-bit) registers are still sufficient for CPU-based tasks.
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Practical, pragmatic use of XMM registers include:
* Cuckoo Hashing (See: https://github.com/stanford-futuredata/index-baselines/blob/...) -- Have 8-bins per hash value for a total of 16-bins. Use SIM
Read the rest
D to perform 8x comparisons at once.
* Huge number of database applications: http://www.cs.columbia.edu/~orestis/sigmod15.pdf
Bloom Filters are the most obvious "SIMD" data-structure, with applications to databases and many other tasks. Sorting networks are best implemented in SIMD.
* See this discussion: https://news.ycombinator.com/item?id=16171806
In effect, you have Base64 encoding / decoding that is faster than a PCIe x16 slot. You can encode / decode Base64 using AVX registers faster than you can even pipe data to the GPU.
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True, the GPU is the ultimate SIMD processor. But in many cases, the SIMD task is too fast to go to the GPU. In particular, the Base64 encoder was encoding 20GB/s, while PCIe can only transport 15.6GB/s!! The CPU is done before the data even gets to the GPU.
Ditto with latency-specific code, like Cuckoo Hashing. SIMD speeds up the overall hash-table, but you're only parallel by 8x. There's no point to actually offload a Cuckoo Hash to the GPU.
In effect, you look for "small" parallelism of size 8 to 16 or so, and that's where AVX / AVX2 / AVX512 really shines. Its too expensive to move to the GPU, but you still get a HUGE speedup when you process it on the CPU.