On Wed, 22 Jan 2025 09:57:15 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 remembers and reuses up to two small intermediate
>> buffers per carrier-thread in subsequent calls.
>>
>> 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 10 3.291 ? 0.031 ns/op
>> CallOverheadByValue.byValue avgt 10 5.464 ? 0.007 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:
>
> Back buffer allocation with a single carrier-local segment.
src/java.base/share/classes/jdk/internal/foreign/abi/SharedUtils.java line 389:
> 387: @Override
> 388: protected BufferStack initialValue() {
> 389: return new BufferStack(Arena.ofAuto().allocate(256));
Could as well use keep using TerminatingThreadLocal+Unsafe here, I just like
the fact to use as few non-public apis as possible.
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23142#discussion_r1925044684
