You are viewing a plain text version of this content. The canonical link for it is here.
Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2022/06/09 20:17:44 UTC
[GitHub] [arrow-rs] jhorstmann opened a new issue, #1829: AVX512 + simd binary and/or kernels slower than autovectorized version
jhorstmann opened a new issue, #1829:
URL: https://github.com/apache/arrow-rs/issues/1829
**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
Related to extending the tests for different features flags #1822, I wanted to take another look at the avx512 feature and its performance. Benchmarks were run on an i9-11900KB @ 3Ghz (turbo disabled) with
```
RUSTFLAGS="-Ctarget-cpu=native -Ctarget-feature=-prefer-256-bit"
```
(the second flag might require some explanation, it **disables** the `prefer-256-bit` feature, which makes llvm use the full 512 bit vectors)
For some reason the second benchmark is always significantly slower when run together, running them separately gives the same (higher) performance and the assembly looks identical except for the and/or. I'm guessing branch predictor or allocator related.
## Default features
```
$ cargo +nightly bench --bench buffer_bit_ops
buffer_bit_ops/buffer_bit_ops and
time: [134.57 ns 134.90 ns 135.28 ns]
thrpt: [105.74 GiB/s 106.04 GiB/s 106.30 GiB/s]
buffer_bit_ops/buffer_bit_ops or
time: [275.55 ns 276.22 ns 277.03 ns]
thrpt: [51.637 GiB/s 51.789 GiB/s 51.914 GiB/s]
```
## Simd feature
```
$ cargo +nightly bench --features simd --bench buffer_bit_ops
buffer_bit_ops/buffer_bit_ops and
time: [168.90 ns 169.10 ns 169.32 ns]
thrpt: [84.486 GiB/s 84.596 GiB/s 84.697 GiB/s]
buffer_bit_ops/buffer_bit_ops or
time: [303.13 ns 303.27 ns 303.45 ns]
thrpt: [47.142 GiB/s 47.169 GiB/s 47.192 GiB/s]
```
## Avx512 feature
```
$ cargo +nightly bench --features avx512 --bench buffer_bit_ops --
buffer_bit_ops/buffer_bit_ops and
time: [165.46 ns 165.95 ns 166.83 ns]
thrpt: [85.745 GiB/s 86.203 GiB/s 86.458 GiB/s]
buffer_bit_ops/buffer_bit_ops or
time: [310.63 ns 311.32 ns 312.04 ns]
thrpt: [45.844 GiB/s 45.950 GiB/s 46.052 GiB/s]
```
Generated assembly for `simd` and `avx512` looks identical, the loop calculates 512bits/64 bytes. The auto-vectorized version instead gets unrolled 4 times, which reduces the loop overhead, so each iteration processes 4x512bits.
**Describe the solution you'd like**
With these benchmark results it seems that we can remove the `avx512` feature and simplify the buffer code.
**Describe alternatives you've considered**
An `avx512` feature for other kernels would still be very useful. Avx512 for example has instructions that basically implement the filter kernel for primitives in a single instruction and it is unlikely that these will be supported in a portable way soon (https://github.com/rust-lang/portable-simd/issues/240).
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: github-unsubscribe@arrow.apache.org.apache.org
For queries about this service, please contact Infrastructure at:
users@infra.apache.org
[GitHub] [arrow-rs] tatsuya6502 commented on issue #1829: AVX512 + simd binary and/or kernels slower than autovectorized version
Posted by GitBox <gi...@apache.org>.
tatsuya6502 commented on issue #1829:
URL: https://github.com/apache/arrow-rs/issues/1829#issuecomment-1152036764
> For some reason the second benchmark is always significantly slower when run together, running them separately gives the same (higher) performance and the assembly looks identical except for the and/or. I'm guessing branch predictor or allocator related.
You might want to do some sampling on CPU frequencies using `lscpu -e` or something while running these benchmarks. Since AVX-512 SIMD instructions consume much more power than regular 64 byte instructions (registers are eight times longer), they can produce more heat and CPU cores can reduce the base frequencies.
This article by Cloudflare explains about accidental AVX-512 throttling:
https://blog.cloudflare.com/on-the-dangers-of-intels-frequency-scaling/
Note that the article was written in 2017, and today's processors could do better than that. I am not sure if it still applies or not.
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: github-unsubscribe@arrow.apache.org
For queries about this service, please contact Infrastructure at:
users@infra.apache.org
[GitHub] [arrow-rs] nevi-me closed issue #1829: AVX512 + simd binary and/or kernels slower than autovectorized version
Posted by GitBox <gi...@apache.org>.
nevi-me closed issue #1829: AVX512 + simd binary and/or kernels slower than autovectorized version
URL: https://github.com/apache/arrow-rs/issues/1829
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: github-unsubscribe@arrow.apache.org
For queries about this service, please contact Infrastructure at:
users@infra.apache.org
[GitHub] [arrow-rs] jhorstmann commented on issue #1829: AVX512 + simd binary and/or kernels slower than autovectorized version
Posted by GitBox <gi...@apache.org>.
jhorstmann commented on issue #1829:
URL: https://github.com/apache/arrow-rs/issues/1829#issuecomment-1151583367
The auto-vectorized version of and/or with non-zero offsets amazingly also runs at about 50 GiB/s
--
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
To unsubscribe, e-mail: github-unsubscribe@arrow.apache.org
For queries about this service, please contact Infrastructure at:
users@infra.apache.org