RFR: 8351999: JFR: Incorrect scaling of throttled values

[Erik Gahlin]

On Fri, 14 Mar 2025 12:16:40 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Could I have a review of a PR that fixes an incorrect scaling of samples for the ThrottleSetting.
>> 
>> Testing: jdk/jdk/jfr
>> 
>> Thanks
>> Erik
>
> src/jdk.jfr/share/classes/jdk/jfr/internal/settings/ThrottleSetting.java line 97:
> 
>> 95:             if (unit.nanos < SECONDS.nanos) {
>> 96:                 long perSecond = SECONDS.nanos / unit.nanos;
>> 97:                 samples = Utils.multiplyOverflow(samples, perSecond, Long.MAX_VALUE);
> 
> Reasoning from the math alone, it looks obvious that `samples *= samples` is not correct. So that part looks fine.
> 
> Thinking about `unit.nanos == SECONDS.nanos` case. This means the unit is exactly "seconds", so no adjustment is needed?

Native expects the value in milliseconds, and the default value is 1000 ms, so it seems fine to me.

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PR Review Comment: https://git.openjdk.org/jdk/pull/24045#discussion_r1995881185