Integrated: 8252990: Intrinsify Unsafe.storeStoreFence
Aleksey Shipilev
shade at openjdk.java.net
Tue Nov 2 10:29:17 UTC 2021
On Wed, 27 Oct 2021 11:53:47 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:
> `Unsafe.storeStoreFence` currently delegates to stronger `Unsafe.storeFence`. We can teach compilers to map this directly to already existing rules that handle `MemBarStoreStore`. Like explicit `LoadFence`/`StoreFence`, we introduce the special node to differentiate explicit fence and implicit store-store barriers. `storeStoreFence` is usually used to simulate safe `final`-field like constructions in special JDK classes, like `ConstantCallSite` and friends.
>
> Motivational performance difference on benchmarks from JDK-8276054 on ARM32 (Raspberry Pi 4):
>
>
> Benchmark Mode Cnt Score Error Units
> Multiple.plain avgt 3 2.669 ± 0.004 ns/op
> Multiple.release avgt 3 16.688 ± 0.057 ns/op
> Multiple.storeStore avgt 3 14.021 ± 0.144 ns/op // Better
>
> MultipleWithLoads.plain avgt 3 4.672 ± 0.053 ns/op
> MultipleWithLoads.release avgt 3 16.689 ± 0.044 ns/op
> MultipleWithLoads.storeStore avgt 3 14.012 ± 0.010 ns/op // Better
>
> MultipleWithStores.plain avgt 3 14.687 ± 0.009 ns/op
> MultipleWithStores.release avgt 3 45.393 ± 0.192 ns/op
> MultipleWithStores.storeStore avgt 3 38.048 ± 0.033 ns/op // Better
>
> Publishing.plain avgt 3 27.079 ± 0.201 ns/op
> Publishing.release avgt 3 27.088 ± 0.241 ns/op
> Publishing.storeStore avgt 3 27.009 ± 0.259 ns/op // Within error, hidden by allocation
>
> Single.plain avgt 3 2.670 ± 0.002 ns/op
> Single.releaseFence avgt 3 6.675 ± 0.001 ns/op
> Single.storeStoreFence avgt 3 8.012 ± 0.027 ns/op // Worse, seems to be ARM32 implementation artifact
>
>
> The same thing on AArch64 (Raspberry Pi 3):
>
>
> Benchmark Mode Cnt Score Error Units
>
> Multiple.plain avgt 3 5.914 ± 0.115 ns/op
> Multiple.release avgt 3 10.149 ± 0.059 ns/op
> Multiple.storeStore avgt 3 6.757 ± 0.138 ns/op // Better
>
> MultipleWithLoads.plain avgt 3 11.849 ± 0.331 ns/op
> MultipleWithLoads.release avgt 3 35.565 ± 1.144 ns/op
> MultipleWithLoads.storeStore avgt 3 19.441 ± 0.471 ns/op // Better
>
> MultipleWithStores.plain avgt 3 5.920 ± 0.213 ns/op
> MultipleWithStores.release avgt 3 20.286 ± 0.347 ns/op
> MultipleWithStores.storeStore avgt 3 12.686 ± 0.230 ns/op // Better
>
> Publishing.plain avgt 3 22.261 ± 1.630 ns/op
> Publishing.release avgt 3 22.269 ± 0.576 ns/op
> Publishing.storeStore avgt 3 17.464 ± 0.397 ns/op // Better
>
> Single.plain avgt 3 5.916 ± 0.063 ns/op
> Single.release avgt 3 10.148 ± 0.401 ns/op
> Single.storeStore avgt 3 6.767 ± 0.164 ns/op // Better
>
>
> As expected, this does not affect x86_64 at all, because both `release` and `storeStore` are effectively no-ops, only affecting compiler optimizations:
>
>
> Benchmark Mode Cnt Score Error Units
>
> Multiple.plain avgt 3 0.406 ± 0.002 ns/op
> Multiple.release avgt 3 0.409 ± 0.018 ns/op
> Multiple.storeStore avgt 3 0.406 ± 0.001 ns/op
>
> MultipleWithLoads.plain avgt 3 4.328 ± 0.006 ns/op
> MultipleWithLoads.release avgt 3 4.600 ± 0.014 ns/op
> MultipleWithLoads.storeStore avgt 3 4.602 ± 0.006 ns/op
>
> MultipleWithStores.plain avgt 3 0.812 ± 0.001 ns/op
> MultipleWithStores.release avgt 3 0.812 ± 0.002 ns/op
> MultipleWithStores.storeStore avgt 3 0.812 ± 0.002 ns/op
>
> Publishing.plain avgt 3 6.370 ± 0.059 ns/op
> Publishing.release avgt 3 6.358 ± 0.436 ns/op
> Publishing.storeStore avgt 3 6.367 ± 0.054 ns/op
>
> Single.plain avgt 3 0.407 ± 0.039 ns/op
> Single.releaseFence avgt 3 0.406 ± 0.001 ns/op
> Single.storeStoreFence avgt 3 0.406 ± 0.001 ns/op
>
>
> Additional testing:
> - [x] Linux x86_64 fastdebug `tier1`
> - [x] Linux AArch64 fastdebug `tier1`
> - [x] Linux x86_64 Fences benchmark
> - [x] Linux AArch64 Fences benchmark
> - [x] Linux ARM32 Fences benchmark
> - [x] Linux AArch64 jcstress `quick` run
This pull request has now been integrated.
Changeset: b7a06be9
Author: Aleksey Shipilev <shade at openjdk.org>
URL: https://git.openjdk.java.net/jdk/commit/b7a06be98d3057dac4adbb7f4071ac62cf88fe52
Stats: 38 lines in 16 files changed: 32 ins; 5 del; 1 mod
8252990: Intrinsify Unsafe.storeStoreFence
Reviewed-by: dholmes, thartmann, whuang
-------------
PR: https://git.openjdk.java.net/jdk/pull/6136
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