RFR: 8318709: Improve System.nanoTime performance on Windows [v2]

[David Holmes]

On Thu, 26 Oct 2023 07:25:48 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

>> - use LARGE_INTEGER.QuadPart instead of assembling the jlong from high/low parts
>> - precalculate counts_per_nano to avoid costly floating-point division in counter to nanosecond conversion
>> 
>> Benchmark before:
>> SystemTime.nanoTime                avgt   15  19,366 � 0,383  ns/op
>> 
>> After:
>> SystemTime.nanoTime                avgt   15  15,812 � 0,385  ns/op
>> 
>> Tier1-2 clean.
>
> Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix variable name

Looks good. Thanks for this optimization!

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Marked as reviewed by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/16336#pullrequestreview-1698955056