RFR: 8268098: jdk.CPULoad event reports incorrect CPU usage inside a container

[Yasumasa Suenaga]

jdk.CPULoad event reports CPU usage.
If JVM runs in a container which is limited CPU resource (quota, shares, cpu), it is incorrect.

When I ran following program inside a container with `--cpuset-cpu=0,1`, I expected jdk.CPULoad event reports 50%, however it reported 25% because container host has 4 CPUs.


public class InfiniteLoop{
  public static void main(String[] args){
    while(true){
    }
  }
}


jdk.CPULoad event uses the result from `get_cpu_load()` in os_perf_linux.cpp, but it does not consider cgroups.

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Commit messages:
 - 8268098: jdk.CPULoad event reports incorrect CPU usage inside a container

Changes: https://git.openjdk.java.net/jdk/pull/4299/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4299&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268098
  Stats: 24 lines in 1 file changed: 21 ins; 2 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4299.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4299/head:pull/4299

PR: https://git.openjdk.java.net/jdk/pull/4299