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List:       openjdk-hotspot-compiler-dev
Subject:    Re: RFR: 8320649: C2: Optimize scoped values [v9]
From:       Andrew Haley <aph () openjdk ! org>
Date:       2024-02-29 16:02:50
Message-ID: v4EUPUrFOT_NNByKsaXFBOB953Di-yAX2KcLZv617h0=.67a636d8-d193-4839-a77c-0f26a9591a84 () github ! com
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On Mon, 26 Feb 2024 16:18:17 GMT, Emanuel Peter <epeter@openjdk.org> wrote:

> Ah, one more thing: what about a JMH benchmark where you can show off how much this \
> optimization improves runtime? ;)

We already have benchmarks, but the biggest win due to this change is the opportunity \
to reduce the load on the scoped value cache.

At present, high performance depends on the per-thread cache, which is a 16-element \
OOP array. This is a fairly heavyweight structure for virtual threads, which \
otherwise have a very small heap footprint. With this optimization I think I can \
shrink the cache without significant loss of performance in most cases. I might also \
be able to move this cache to the carrier thread.

So, this patch significantly moves the balance point in the space/speed tradeoff.

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

PR Comment: https://git.openjdk.org/jdk/pull/16966#issuecomment-1971449329


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