RFR: 8265836: OperatingSystemImpl.getCpuLoad() returns incorrect CPU load inside a container [v2]

[Severin Gehwolf]

On Tue, 11 May 2021 14:57:32 GMT, Hao Tang <github.com+7947546+tanghaoth90 at openjdk.org> wrote:

>> OperatingSystemImpl.getCpuLoad() may return 1.0 in a container, even though the CPU load is obviously below 100%.
>> 
>> We created a 5-core container and run 4 "while (true)" loops in the container. OperatingSystemImpl.getCpuLoad() returned 1.0, which is incorrect (0.8 is correct).
>> "systemLoad" in getCpuLoad() is exactly 4.0 before "systemLoad = Math.min(1.0, systemLoad);". The problem is caused by using the elapsed time (specified by "cpu.cfs_period_us") instead of the total CPU time (specified by "cpu.cfs_quota_us"). Therefore, it is more reasonable to divide cpu usage time by "quotaNanos" instead of "elapsedNanos".
>
> Hao Tang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   cpu.shares for OperatingSystemImpl.getCpuLoad()

@tanghaoth90 I've added a comment which should address the cpu shares based cpuLoad problem. Let me know what you think.

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PR: https://git.openjdk.java.net/jdk/pull/3656