RFR: 8337269: G1ConfidencePercent interpreted inconsistently

[Kim Barrett]

On Thu, 10 Oct 2024 09:56:58 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this change that removes the inconsistency in interpretation of G1ConfidencePercent; higher confidence means that G1 should use less safety margin (i.e. part of the variance).
> 
> Other than that it does not change the uses for it.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Retracting my prior approval.

I think the proposed change does address the described inconsistency.  But I
think it doesn't go far enough.

The G1Predictions constructor takes a "sigma" argument.  It range checks it,
and the failure message describes it as "confidence".  The accessor for that
value is described as "Confidence factor".  That seems inconsistent with the
usage (a small value suggests higher confidence in the average value), and
with the new calculation of the argument.

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Changes requested by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/21448#pullrequestreview-2361702801