RFR: 8265836: OperatingSystemImpl.getCpuLoad() returns incorrect CPU load

[Argha C]

On Wed, 5 May 2021 05:57:55 GMT, Hao Tang <github.com+7947546+tanghaoth90 at openjdk.org> wrote:

>> src/jdk.management/unix/classes/com/sun/management/internal/OperatingSystemImpl.java line 142:
>> 
>>> 140:                 long usageNanos = containerMetrics.getCpuUsage();
>>> 141:                 if (numPeriods > 0 && usageNanos > 0) {
>>> 142:                     long quotaNanos = TimeUnit.MICROSECONDS.toNanos(quota * numPeriods);
>> 
>> We happened to hit an exactly similar problem when running on a container with openjdk15.
>> 
>> Given we effectively agree that the problem is `elapsedNanos` doesn't accurately reflect the cpu time allocated across all shares vs a single share, my proposal was to use `getCpuShares` as a multiplier for `periodLength` above. 
>> Is there a good reason `getCpuQuota` is a better alternative?
>
> Hi Argha, thanks a lot for your suggestion. I think both "quota" and "share" are worth considering. Let us look into the implementation of `CgroupSubsystem::active_processor_count()` in OpenJDK HotSpot (https://github.com/openjdk/jdk/blob/master/src/hotspot/os/linux/cgroupSubsystem_linux.cpp).

Thanks for linking that. It sounds reasonable to me to prefer `quota` in that case.

-------------

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