On Thu, 23 Jan 2025 17:36:11 GMT, Matthias Ernst <d...@openjdk.org> wrote:
>> Certain signatures for foreign function calls (e.g. HVA return by value) >> require allocation of an intermediate buffer to adapt the FFM's to the >> native stub's calling convention. In the current implementation, this buffer >> is malloced and freed on every FFM invocation, a non-negligible overhead. >> >> Sample stack trace: >> >> java.lang.Thread.State: RUNNABLE >> at jdk.internal.misc.Unsafe.allocateMemory0(java.base@25-ea/Native >> Method) >> ... >> at >> jdk.internal.foreign.abi.SharedUtils.newBoundedArena(java.base@25-ea/SharedUtils.java:386) >> at >> jdk.internal.foreign.abi.DowncallStub/0x000001f001084c00.invoke(java.base@25-ea/Unknown >> Source) >> ... >> at >> java.lang.invoke.Invokers$Holder.invokeExact_MT(java.base@25-ea/Invokers$Holder) >> >> >> To alleviate this, this PR implements a per carrier-thread stacked allocator. >> >> Performance (MBA M3): >> >> >> Before: >> Benchmark Mode Cnt Score Error Units >> CallOverheadByValue.byPtr avgt 10 3.333 ? 0.152 ns/op >> CallOverheadByValue.byValue avgt 10 33.892 ? 0.034 ns/op >> >> After: >> Benchmark Mode Cnt Score Error Units >> CallOverheadByValue.byPtr avgt 30 3.311 ? 0.034 ns/op >> CallOverheadByValue.byValue avgt 30 6.143 ? 0.053 ns/op >> >> >> `-prof gc` also shows that the new call path is fully scalar-replaced vs 160 >> byte/call before. > > Matthias Ernst has updated the pull request incrementally with one additional > commit since the last revision: > > fix test under VThread factory As to what's causing the issue, I wonder if the stack buffer is being freed while it is still in use, somehow. We reinterpret the segment from the shared arena, maybe the frame should keep that arena alive until it is closed itself (with a `Reference.reachabilityFence`). Looking at the code, the shared per-thread arena should be strongly reachable though, so I'm not sure if that is a plausible explanation... ------------- PR Comment: https://git.openjdk.org/jdk/pull/23142#issuecomment-2627576484
