Summary:
Crc32c Parallel computation coding optimization:
Macro unfolding removes the "for" loop and is good to decrease branch-miss in arm64 micro architecture
1024 Bytes is divided into 8(head) + 1008( 6 * 7 * 3 * 8 ) + 8(tail) three parts
Macro unfolding 42 loops to 6 CRC32C7X24BYTESs
1 CRC32C7X24BYTES containing 7 CRC32C24BYTESs
1, crc32c_test
[==========] Running 4 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 4 tests from CRC
[ RUN ] CRC.StandardResults
[ OK ] CRC.StandardResults (1 ms)
[ RUN ] CRC.Values
[ OK ] CRC.Values (0 ms)
[ RUN ] CRC.Extend
[ OK ] CRC.Extend (0 ms)
[ RUN ] CRC.Mask
[ OK ] CRC.Mask (0 ms)
[----------] 4 tests from CRC (1 ms total)
[----------] Global test environment tear-down
[==========] 4 tests from 1 test case ran. (1 ms total)
[ PASSED ] 4 tests.
2, db_bench --benchmarks="crc32c"
crc32c : 0.218 micros/op 4595390 ops/sec; 17950.7 MB/s (4096 per op)
3, repeated crc32c_test case 60000 times
perf stat -e branch-miss -- ./crc32c_test
before optimization:
739,426,504 branch-miss
after optimization:
1,128,572 branch-miss
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5675
Differential Revision: D16989210
fbshipit-source-id: 7204e6069bb6ed066d49c2d1b3ac385065a98557
Summary:
Crc32c Parallel computation optimization:
Algorithm comes from Intel whitepaper: [crc-iscsi-polynomial-crc32-instruction-paper](https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/crc-iscsi-polynomial-crc32-instruction-paper.pdf)
Input data is divided into three equal-sized blocks
Three parallel blocks (crc0, crc1, crc2) for 1024 Bytes
One Block: 42(BLK_LENGTH) * 8(step length: crc32c_u64) bytes
1. crc32c_test:
```
[==========] Running 4 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 4 tests from CRC
[ RUN ] CRC.StandardResults
[ OK ] CRC.StandardResults (1 ms)
[ RUN ] CRC.Values
[ OK ] CRC.Values (0 ms)
[ RUN ] CRC.Extend
[ OK ] CRC.Extend (0 ms)
[ RUN ] CRC.Mask
[ OK ] CRC.Mask (0 ms)
[----------] 4 tests from CRC (1 ms total)
[----------] Global test environment tear-down
[==========] 4 tests from 1 test case ran. (1 ms total)
[ PASSED ] 4 tests.
```
2. RocksDB benchmark: db_bench --benchmarks="crc32c"
```
Linear Arm crc32c:
crc32c: 1.005 micros/op 995133 ops/sec; 3887.2 MB/s (4096 per op)
```
```
Parallel optimization with Armv8 crypto extension:
crc32c: 0.419 micros/op 2385078 ops/sec; 9316.7 MB/s (4096 per op)
```
It gets ~2.4x speedup compared to linear Arm crc32c instructions.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5494
Differential Revision: D16340806
fbshipit-source-id: 95dae9a5b646fd20a8303671d82f17b2e162e945
DaiZhiwei