On Mon, 23 May 2022 16:05:16 GMT, Dmitry Chuyko <dchu...@openjdk.org> wrote:
>> On AArch64 it is sometimes convenient to have LSE atomics right from the >> start. Currently they are enabled after feature detection and RR reverse >> debugger works incorrectly. >> >> New build configuration feature 'hardlse' is added. If it is enabled for >> aarch64 type of build, then statically compiled stubs replace the initial >> pessimistic implementation and dynamically generated replacements (when LSE >> support is detected). The feature works for builds of all debug levels. >> >> New file atomic_linux_aarch64_lse.S is derived from atomic_linux_aarch64.S >> and inherits its copyright. This alternative static implementation >> corresponds to the dynamically generated code. >> >> Note, this configuration part is necessary but not sufficient to fully avoid >> strex instructions for practical purposes. Other parts are: >> >> * Run on the OS built without strex family instructions. E.g. Amazon Linux >> 2022. >> * Compile with outline atomics enabled and the configuration flag enabled. >> E.g. configure with >> --with-extra-cflags='-march=armv8.3-a+crc+crypto -moutline-atomics' >> --with-extra-cxxflags='-march=armv8.3-a+crc+crypto -moutline-atomics' >> --with-extra-ldflags='-Wl,--allow-multiple-definition' >> --with-jvm-features=hardlse >> >> Testing: tier1, tier2 on linux-aarch64 release builds with feature off and >> feature on. > > Dmitry Chuyko has updated the pull request incrementally with two additional > commits since the last revision: > > - Use LSE in linux-aarch64 asm code if __ARM_FEATURE_ATOMICS is on > - Revert "hardlse feature" > > This reverts commit c5da85d3282bb995f69639f8f592cc94560916c5. New variant turns on using LSE atomics statically when __ARM_FEATURE_ATOMICS compiler feature is on. Prefetch is left only to non-LSE case, the kernel seems to do the same. ------------- PR: https://git.openjdk.java.net/jdk/pull/8779
