Multi-buffer sha256 support in SPL to ZFS

[dong-liuliu]

This patch implements multi-buffer hash facilities to export a general
SHA256 api to ZFS. When multibuffer hash is configured in SPL, its
SHA256 api for ZFS will automaticlly transfer SHA256 compute task to
multi-buffer hash facilities which will increase SHA256 performance
2~7 times.

ISA-L multi-buffer hash provides software acceleration for SHA256:
https://github.com/01org/isa-l_crypto

• To enable multi-buffer hash acceleration, you need to download ISA-L
  crypto lib source code from above link and checkout master branch.
• Configure multi-buffer hash in SPL, e.g.:
  ./configure --with-hash-mb=
  make
  Following make notice, run:
  make -C -f Makefile.kern kernobj
  Then, continue run:
  make
• After that, a C predefine marco HAVE_HASH_MB and C api mulbuf_sha256
  will be exported out to ZFS module

If ZFS is also patched with multi-buffer sha256, then.
Set sha256 checksum in ZFS dataset: "checksum = sha256"
Data written to ZFS pool will be checksumed by multi-buffer sha256.
Run write workload, on Intel Xeon of Haswell type, cpu consumption of
sha256 will be decreased to be previous 1/2~1/5.

Multibuffer sha256 follows standard sha256 format. With SIMD instruction
set, it can process 4/8/16 sha256 tasks simutaneously. So it has a much
better compute throughput.
Here are Isa-L's performance data sheets about multi-buffer hash.

Intel® Xeon® E5-2600v3 (Haswell)
Hash functions	ISA-L multi-buffer version	OpenSSL single version
SHA-1	1.9 GB/s	542 MB/s
SHA-256	881 MB/s	183 MB/s
SHA-512	689 MB/s	286 MB/s
MD5	3.7 GB/s	465 MB/s

Intel® Xeon® Platinum 8180 (Skylake)
Hash functions	ISA-L multi-buffer version	OpenSSL single version
SHA-1	5.4 GB/s	605 MB/s
SHA-256	2.7 GB/s	216 MB/s
SHA-512	2.2 GB/s	334 MB/s
MD5	9.7 GB/s	401 MB/s

[tonyhutter]

Does the performance stay the same if you're using an older-than-Haswell CPU?

[dong-liuliu]

On Xeon Sandy Bridge or Ivy Bridge, it is still better. On others, it should be the same.

[behlendorf]

@dong-liuliu sorry about the delay but the spl has now been merged to the zfs repository. If you're still interested in getting this support included please go ahead and open a new PR against ZFS.

[thegreatgazoo]

I thought isa-l_crypto was a user-space library. If I was not wrong, could you please describe how SPL could use that library from the kernel?

[dong-liuliu]

Yes, originally, it's a user-space library. Since it only do computing without further logical operations, it is easy to port isa-l_crypto into kernel env with a wrapper layer.

[thegreatgazoo]

@dong-liuliu is there an official kernel port already? Thanks!