RFR: 8324186: AARCH64: Use "dmb.ishst+dmb.ishld" for release barrier

[Andrew Haley]

On Mon, 22 Jan 2024 01:58:32 GMT, kuaiwei <duke at openjdk.org> wrote:

> Details is https://mail.openjdk.org/pipermail/hotspot-compiler-dev/2024-January/071921.html.
> Using a combined dmb.ish for release barrier will introduce a heavy storeload barrier. Use "dmb.ishst+dmb.ishld" pair instead, we can gain performance improvement on N1 and N2 architecture. The benchmark is test/micro/org/openjdk/bench/vm/compiler/FinalFieldInitialize.java
> Run with ParallelGC to minimalize impact of gc barrier.
> 
> make test TEST="micro:org.openjdk.bench.vm.compiler.FinalFieldInitialize" MICRO="VM_OPTIONS=-XX:+UseParallelGC"
> ...
> FinalFieldInitialize.testAllocWithFinal  thrpt    9  1411.601 ?  6.546  ops/s
> 
> Without the patch
> 
> FinalFieldInitialize.testAllocWithFinal  thrpt    9  1214.575 ? 14.217  ops/s

Very nice. Thanks.

src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 2069:

> 2067:   if (last != nullptr && nativeInstruction_at(last)->is_Membar() && prev == last) {
> 2068:     NativeMembar *bar = NativeMembar_at(prev);
> 2069:     // We need avoid promoting barrier to dmb.ish,

Suggestion:

    // Don't promote DMB ST|DMB LD to DMB (a full barrier) because
    // doing so would introduce  a StoreLoad which  the caller did not
    // intend.

I think that should be clear enough.

-------------

Marked as reviewed by aph (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17511#pullrequestreview-1836113464
PR Review Comment: https://git.openjdk.org/jdk/pull/17511#discussion_r1461628025