On Wed, 22 Nov 2023 02:09:38 GMT, David Holmes <dhol...@openjdk.org> wrote:
>> As discussed in JBS all platforms (some tweaks to Zero are in progress) >> actually do support `cx8` i.e. 64-bit compare-and-exchange, so we can strip >> out the locked-based alternatives to using it and just add a guarantee that >> it is true at runtime. And all platforms except some ARM variants set >> `SUPPORTS_NATIVE_CX8`, so we can greatly simplify things. Summary of changes: >> - `_supports_cx8` field is only needed when `SUPPORTS_NATIVE_CX8` is not >> defined >> - Assertions for `supports_cx8()` are removed >> - Compiler predicates requiring `supports_cx8()` are removed >> - Access backend is greatly simplified without the need for lock-based >> alternative >> - `java.util.concurrent.AtomicLongFieldUpdater` is simplified without the >> need for a lock-based alternative >> >> I did consider moving all the ARM `kuser_helper` related code to be only >> defined when `SUPPORTS_NATIVE_CX8` is not defined, but there was a >> theoretical risk this could change the behaviour if ARMv7 binaries were run >> on other ARM CPU's. I added a note to that effect in >> vm_version_linux_arm32.cpp so the ARM port maintainers could clean this up >> further if desired. >> >> Testing: >> - All Oracle tiers 1-5 builds (which includes an ARMv7 build) >> - GHA builds/tests >> - Oracle tiers 1-3 sanity testing >> >> Zero changes coming in via >> [JDK-8319777](https://bugs.openjdk.org/browse/JDK-8319777) will be merged >> when they arrive. >> >> Thanks. > > David Holmes has updated the pull request with a new target base due to a > merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains seven additional > commits since the last revision: > > - Merge with master and update Zero code accordingly > - Merge branch 'master' into 8318776-supports_cx8 > - Remove unnecessary includes of vm_version.hpp. > Fix copyright years. > - Remove cx8 comment as no longer relevant (the spinlock is used regardless > of cx8) > - Remove suports_cx8() checks from gtest > - Remove test for VMSupportsCX8 > - 8318776: Require supports_cx8 to always be true src/hotspot/share/runtime/vm_version.cpp line 33: > 31: void VM_Version_init() { > 32: VM_Version::initialize(); > 33: guarantee(VM_Version::supports_cx8(), "Support for 64-bit atomic > operations in required in this release"); Typo: "in required in". Also, no need to mention "this release" at all? Suggestion for message: "JVM requires platform support for 64-bit atomic operations" ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/16625#discussion_r1401743607
