On Fri, 30 Aug 2024 09:09:57 GMT, Per Minborg <pminb...@openjdk.org> wrote:
>> The performance of the `MemorySegment::fil` can be improved by replacing the >> `checkAccess()` method call with calling `checkReadOnly()` instead (as the >> bounds of the segment itself do not need to be checked). >> >> Also, smaller segments can be handled directly by Java code rather than >> transitioning to native code. >> >> Here is how the `MemorySegment::fill` performance is improved by this PR: >> >>  >> >> Operations involving 8 or more bytes are delegated to native code whereas >> smaller segments are handled via a switch rake. >> >> It should be noted that `Arena::allocate` is using `MemorySegment::fil`. >> Hence, this PR will also have a positive effect on memory allocation >> performance. > > Per Minborg has updated the pull request incrementally with one additional > commit since the last revision: > > Remove unused imports Changes requested by franz1...@github.com (no known OpenJDK username). src/java.base/share/classes/jdk/internal/misc/X-ScopedMemoryAccess.java.template line 210: > 208: // Handle smaller segments directly without > transitioning to native code > 209: final long u = Byte.toUnsignedLong(value); > 210: final long longValue = u << 56 | u << 48 | u << 40 | u > << 32 | u << 24 | u << 16 | u << 8 | u; this can be `u * 0xFFFFFFFFFFFFL` if `value != 0` and just `0L` if not: not sure if fast(er), need to measure. Most of the time filling is happy with 0 since zeroing is the most common case ------------- PR Review: https://git.openjdk.org/jdk/pull/20712#pullrequestreview-2271723714 PR Review Comment: https://git.openjdk.org/jdk/pull/20712#discussion_r1738292680
