On Tue, 26 Nov 2024 13:55:10 GMT, Viktor Klang <vkl...@openjdk.org> wrote:
>> This PR proposes adding a _JDK-internal_ method for calculating hash codes >> for content in a `MemorySegment`. >> >> The internal method uses a polynomial 32-bit hash function equivalent to >> `Arrays::hashCode`. The new method is almost two times faster than naïvely >> iterating over individual bytes for larger regions. Also, it is more lean on >> inlining space compared to a naïve loop. >> >> >> >> Benchmark (ELEM_SIZE) Mode Cnt Score Error >> Units >> SegmentBulkHash.array 8 avgt 30 2.645 ? 0.078 >> ns/op >> SegmentBulkHash.array 64 avgt 30 6.062 ? 0.171 >> ns/op >> SegmentBulkHash.heapSegment 8 avgt 30 4.181 ? 0.145 >> ns/op >> SegmentBulkHash.heapSegment 64 avgt 30 25.716 ? 1.043 >> ns/op >> SegmentBulkHash.nativeSegment 8 avgt 30 3.939 ? 0.150 >> ns/op >> SegmentBulkHash.nativeSegment 64 avgt 30 23.262 ? 0.694 >> ns/op >> SegmentBulkHash.nativeSegmentJava 8 avgt 30 5.219 ? 0.183 >> ns/op <- Naïve iteration >> SegmentBulkHash.nativeSegmentJava 64 avgt 30 39.668 ? 1.040 >> ns/op <- Naïve iteration >> >> >>  >> >> >> If internal JDK code uses this method, it will automatically benefit from >> future performance improvements that can be implemented once the Vector API >> becomes available. > > src/java.base/share/classes/jdk/internal/foreign/SegmentBulkOperations.java > line 208: > >> 206: final long limit = fromOffset + longBytes; >> 207: for (; fromOffset < limit; fromOffset += 8) { >> 208: long val = >> SCOPED_MEMORY_ACCESS.getLongUnaligned(segment.sessionImpl(), >> segment.unsafeGetBase(), segment.unsafeGetOffset() + fromOffset, >> !Architecture.isLittleEndian()); > > @minborg Does it help to hoist the calls to `segment.sessionImpl()` + > `segment.unsafeGetBase()` + `segment.unsafeGetOffset()` + > `!Architecture.isLittleEndian()` and reusing those throughout the different > strides? I thought that initially as well, but keeping it like this helps the compiler select the correct unsafe code path. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/22364#discussion_r1858596703
