RFR: 8265836: OperatingSystemImpl.getCpuLoad() returns incorrect CPU load inside a container [v6]

[Severin Gehwolf]

On Thu, 27 May 2021 00:47:23 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

> I haven't followed yet all of discussions in this review, but I concern this PR changes the meaning of `getCpuLoad()`.

Does it? Here is the javadoc:
https://docs.oracle.com/en/java/javase/16/docs/api/jdk.management/com/sun/management/OperatingSystemMXBean.html#getCpuLoad()

It says:

Returns the "recent cpu usage" for the operating environment. This value is a double in the [0.0,1.0] interval.


If I run outside a container, getCpuLoad0() is being used which uses a similar calculation. So in my book this fixes the bug (earlier reporting is just plain wrong, see bug for details) and just brings it in line with the non-container values.

Also note that the cpu quota-based limits implementation as been changed to also report recent load values. But I'm not sure it's worth discussing this further as the previous implementation (supposedly reporting an average) was wrong.

> `getCpuLoad()` has been based on total time since the start of the container, but after this PR, it is based on the ticks in earlier call. Is it ok?

IMHO, yes as the previous implementation was incorrect. I suspect nobody noticed until now.

> IMHO it can be accepted because it is the same with load average on Linux, but I concern we may need CSR because this PR changes behavior.

I disagree. This change makes `getCpuLoad()` behave similar in all cases: non-container case[1], cpu affinity-based[2], cpu-quota-based[3] and cpu-shares based[3] cpu-limits. That wasn't previously the case.

[1] https://bugs.openjdk.java.net/browse/JDK-8265836?focusedCommentId=14423632&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14423632
[2] https://bugs.openjdk.java.net/browse/JDK-8265836?focusedCommentId=14423633&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14423633
[3] https://bugs.openjdk.java.net/browse/JDK-8265836?focusedCommentId=14423371&page=com.atlassian.jira.plugin.system.issuetabpanels%3Acomment-tabpanel#comment-14423371

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