> Hello, > > Today much of the reading of flattened values in the interpreter is > implemented both in the platform-specific templateTable_XX.cpp files, and > also in the runtime via InterpreterRuntime::read_flat_field. The reason we > have both is becuase the interpreterlet implements a fast-path for null-free > types, which attempts to allocate the buffered object inside the thread's > TLAB, before moving on to copy the src payload to the buffered objected. The > copying is done in the VM via a call_VM_leaf call, which notably does not > safepoint-poll (nor allow anything that might GC for example). > > The slow-path in the interpreterlet calls into the VM via a call_VM, which > notably safepoint-point polls upon exit. The slow-path is taken when 1) the > src payload is nullable or 2) the fast-path TLAB allocation fails. > > I propose we redesign the dance around when and how to enter the VM by having > the logic of reading a flat field exclusively inside the runtime and thus > always entering the VM. This approach allows us to have one canonical way to > read flat fields, without having effectively duplicate code in > interpreterlets (for all supported platforms) and inside the runtime. A > benefit from this is that it becomes easier for porters to port the Valhalla > changes to their platform(s) and later on maintain that port, which is a plus. > > Since all objects are NULLABLE in JEP 401 (disregarding F&F interface), all > reads of flat fields are already entering the VM via the "slow-path". This > means that this change only has a practical effect on > null-free/null-restricted fields. I think we should consider if having a > fast-path is worth it or not when that time comes, although I anticipate that > it doesn't make much difference since the copy is always done in the VM > anyway. > > As a small optimization, I've added a check for nullable and marked-as-null > before entering the VM. > > Testing: > * hotspot_valhalla, jdk_valhalla and Oracle's tier1-4 on linux-x64-debug and > linux-aarch64-debug
Joel Sikström has updated the pull request incrementally with one additional commit since the last revision: Dont handle:ize obj in InterpreterRuntime::read_flat_field ------------- Changes: - all: https://git.openjdk.org/valhalla/pull/1936/files - new: https://git.openjdk.org/valhalla/pull/1936/files/61c1f4cf..469258ee Webrevs: - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1936&range=01 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1936&range=00-01 Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod Patch: https://git.openjdk.org/valhalla/pull/1936.diff Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1936/head:pull/1936 PR: https://git.openjdk.org/valhalla/pull/1936
