Integrated: 8359348: G1: Improve cpu usage measurements for heap sizing

[Ivan Walulya]

On Wed, 16 Jul 2025 13:55:32 GMT, Ivan Walulya <iwalulya at openjdk.org> wrote:

> Hi,
> 
> Please review this patch which takes into account the impact of concurrent GC activity on mutator threads when computing the time spent on GC activity in a time interval. Previously, only the GC pause times were considered, and the overhead imposed by concurrent GC worker threads was not included.
> 
> With this change, we now estimate the impact of concurrent GC by dividing `elapsed_gc_cpu_time` by the number of CPUs. This provides an approximation of the additional time attributable to GC activity, assuming a fair CPU resource sharing.  Although this method does not account for contention on other shared resources (such as memory bandwidth or caches), it offers a reasonable estimate for most scenarios.
> 
> Testing: Tier 1

This pull request has now been integrated.

Changeset: 124575b4
Author:    Ivan Walulya <iwalulya at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/124575b4c2b52328a8efddb40e67057a53b44a04
Stats:     77 lines in 5 files changed: 50 ins; 1 del; 26 mod

8359348: G1: Improve cpu usage measurements for heap sizing

Reviewed-by: tschatzl, ayang, manc

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PR: https://git.openjdk.org/jdk/pull/26351