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1# sha256-simd
2
3Accelerate SHA256 computations in pure Go using AVX512, SHA Extensions for x86 and ARM64 for ARM.
4On AVX512 it provides an up to 8x improvement (over 3 GB/s per core).
5SHA Extensions give a performance boost of close to 4x over native.
6
7## Introduction
8
9This package is designed as a replacement for `crypto/sha256`.
10For ARM CPUs with the Cryptography Extensions, advantage is taken of the SHA2 instructions resulting in a massive performance improvement.
11
12This package uses Golang assembly.
13The AVX512 version is based on the Intel's "multi-buffer crypto library for IPSec" whereas the other Intel implementations are described in "Fast SHA-256 Implementations on Intel Architecture Processors" by J. Guilford et al.
14
15## Support for Intel SHA Extensions
16
17Support for the Intel SHA Extensions has been added by Kristofer Peterson (@svenski123), originally developed for spacemeshos [here](https://github.com/spacemeshos/POET/issues/23). On CPUs that support it (known thus far Intel Celeron J3455 and AMD Ryzen) it gives a significant boost in performance (with thanks to @AudriusButkevicius for reporting the results; full results [here](https://github.com/minio/sha256-simd/pull/37#issuecomment-451607827)).
18
19```
20$ benchcmp avx2.txt sha-ext.txt
21benchmark AVX2 MB/s SHA Ext MB/s speedup
22BenchmarkHash5M 514.40 1975.17 3.84x
23```
24
25Thanks to Kristofer Peterson, we also added additional performance changes such as optimized padding,
26endian conversions which sped up all implementations i.e. Intel SHA alone while doubled performance for small sizes,
27the other changes increased everything roughly 50%.
28
29## Support for AVX512
30
31We have added support for AVX512 which results in an up to 8x performance improvement over AVX2 (3.0 GHz Xeon Platinum 8124M CPU):
32
33```
34$ benchcmp avx2.txt avx512.txt
35benchmark AVX2 MB/s AVX512 MB/s speedup
36BenchmarkHash5M 448.62 3498.20 7.80x
37```
38
39The original code was developed by Intel as part of the [multi-buffer crypto library](https://github.com/intel/intel-ipsec-mb) for IPSec or more specifically this [AVX512](https://github.com/intel/intel-ipsec-mb/blob/master/avx512/sha256_x16_avx512.asm) implementation. The key idea behind it is to process a total of 16 checksums in parallel by “transposing” 16 (independent) messages of 64 bytes between a total of 16 ZMM registers (each 64 bytes wide).
40
41Transposing the input messages means that in order to take full advantage of the speedup you need to have a (server) workload where multiple threads are doing SHA256 calculations in parallel. Unfortunately for this algorithm it is not possible for two message blocks processed in parallel to be dependent on one another — because then the (interim) result of the first part of the message has to be an input into the processing of the second part of the message.
42
43Whereas the original Intel C implementation requires some sort of explicit scheduling of messages to be processed in parallel, for Golang it makes sense to take advantage of channels in order to group messages together and use channels as well for sending back the results (thereby effectively decoupling the calculations). We have implemented a fairly simple scheduling mechanism that seems to work well in practice.
44
45Due to this different way of scheduling, we decided to use an explicit method to instantiate the AVX512 version. Essentially one or more AVX512 processing servers ([`Avx512Server`](https://github.com/minio/sha256-simd/blob/master/sha256blockAvx512_amd64.go#L294)) have to be created whereby each server can hash over 3 GB/s on a single core. An `hash.Hash` object ([`Avx512Digest`](https://github.com/minio/sha256-simd/blob/master/sha256blockAvx512_amd64.go#L45)) is then instantiated using one of these servers and used in the regular fashion:
46
47```go
48import "github.com/minio/sha256-simd"
49
50func main() {
51 server := sha256.NewAvx512Server()
52 h512 := sha256.NewAvx512(server)
53 h512.Write(fileBlock)
54 digest := h512.Sum([]byte{})
55}
56```
57
58Note that, because of the scheduling overhead, for small messages (< 1 MB) you will be better off using the regular SHA256 hashing (but those are typically not performance critical anyway). Some other tips to get the best performance:
59* Have many go routines doing SHA256 calculations in parallel.
60* Try to Write() messages in multiples of 64 bytes.
61* Try to keep the overall length of messages to a roughly similar size ie. 5 MB (this way all 16 ‘lanes’ in the AVX512 computations are contributing as much as possible).
62
63More detailed information can be found in this [blog](https://blog.minio.io/accelerate-sha256-up-to-8x-over-3-gb-s-per-core-with-avx512-a0b1d64f78f) post including scaling across cores.
64
65## Drop-In Replacement
66
67The following code snippet shows how you can use `github.com/minio/sha256-simd`.
68This will automatically select the fastest method for the architecture on which it will be executed.
69
70```go
71import "github.com/minio/sha256-simd"
72
73func main() {
74 ...
75 shaWriter := sha256.New()
76 io.Copy(shaWriter, file)
77 ...
78}
79```
80
81## Performance
82
83Below is the speed in MB/s for a single core (ranked fast to slow) for blocks larger than 1 MB.
84
85| Processor | SIMD | Speed (MB/s) |
86| --------------------------------- | ------- | ------------:|
87| 3.0 GHz Intel Xeon Platinum 8124M | AVX512 | 3498 |
88| 3.7 GHz AMD Ryzen 7 2700X | SHA Ext | 1979 |
89| 1.2 GHz ARM Cortex-A53 | ARM64 | 638 |
90
91## asm2plan9s
92
93In order to be able to work more easily with AVX512/AVX2 instructions, a separate tool was developed to convert SIMD instructions into the corresponding BYTE sequence as accepted by Go assembly. See [asm2plan9s](https://github.com/minio/asm2plan9s) for more information.
94
95## Why and benefits
96
97One of the most performance sensitive parts of the [Minio](https://github.com/minio/minio) object storage server is related to SHA256 hash sums calculations. For instance during multi part uploads each part that is uploaded needs to be verified for data integrity by the server.
98
99Other applications that can benefit from enhanced SHA256 performance are deduplication in storage systems, intrusion detection, version control systems, integrity checking, etc.
100
101## ARM SHA Extensions
102
103The 64-bit ARMv8 core has introduced new instructions for SHA1 and SHA2 acceleration as part of the [Cryptography Extensions](http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0501f/CHDFJBCJ.html). Below you can see a small excerpt highlighting one of the rounds as is done for the SHA256 calculation process (for full code see [sha256block_arm64.s](https://github.com/minio/sha256-simd/blob/master/sha256block_arm64.s)).
104
105 ```
106 sha256h q2, q3, v9.4s
107 sha256h2 q3, q4, v9.4s
108 sha256su0 v5.4s, v6.4s
109 rev32 v8.16b, v8.16b
110 add v9.4s, v7.4s, v18.4s
111 mov v4.16b, v2.16b
112 sha256h q2, q3, v10.4s
113 sha256h2 q3, q4, v10.4s
114 sha256su0 v6.4s, v7.4s
115 sha256su1 v5.4s, v7.4s, v8.4s
116 ```
117
118### Detailed benchmarks
119
120Benchmarks generated on a 1.2 Ghz Quad-Core ARM Cortex A53 equipped [Pine64](https://www.pine64.com/).
121
122```
123minio@minio-arm:$ benchcmp golang.txt arm64.txt
124benchmark golang arm64 speedup
125BenchmarkHash8Bytes-4 0.68 MB/s 5.70 MB/s 8.38x
126BenchmarkHash1K-4 5.65 MB/s 326.30 MB/s 57.75x
127BenchmarkHash8K-4 6.00 MB/s 570.63 MB/s 95.11x
128BenchmarkHash1M-4 6.05 MB/s 638.23 MB/s 105.49x
129```
130
131## License
132
133Released under the Apache License v2.0. You can find the complete text in the file LICENSE.
134
135## Contributing
136
137Contributions are welcome, please send PRs for any enhancements.