jmx-dev RFR: 8335625: Update Javadoc for GetCpuLoad

[Joakim Nordström]

Can I get a review of this documentation update to clarify the usage of GetCpuLoad (and inherently deprecated GetSystemCpuLoad) and GetProcessCpuLoad.

Calling either of these methods in quick succession can lead to unrepresentative results due to too few data points.

This behavior is easy to reproduce on at least Linux (Windows implementation enforces a 500 ticks duration); when calling GetCpuLoad repeatedly CPU load values of either 0, 0.5, or 1 will be returned.

double cpuLoad1 = getCpuLoad();
double cpuLoad2 = getCpuLoad();   // not enough ticks has passed to give representative values

Worth noting is that this holds true even if getSystemCpuLoad() is called. 

double cpuLoad1 = getCpuLoad();
double cpuLoad2 = getSystemCpuLoad();   // not enough ticks has passed to give representative values, since getSystemCpuLoad effectively calls getCpuLoad.

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Commit messages:
 - 8335625: Update Javadoc for GetCpuLoad
 - 8335625: Update Javadoc for GetCpuLoad

Changes: https://git.openjdk.org/jdk/pull/20546/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20546&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8335625
  Stats: 14 lines in 1 file changed: 14 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20546.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20546/head:pull/20546

PR: https://git.openjdk.org/jdk/pull/20546