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8216366: Add rationale to PER_CPU_SHARES define

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Reviewed-by: bobv, adinn
This commit is contained in:
Severin Gehwolf 2019-01-08 14:15:14 +01:00
parent 779b2288eb
commit 7d324fc795
1 changed files with 18 additions and 0 deletions
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18
src/hotspot/os/linux/osContainer_linux.cpp
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@ -31,6 +31,24 @@
#include "logging/log.hpp" #include "logging/log.hpp"
#include "osContainer_linux.hpp" #include "osContainer_linux.hpp"
/*
* PER_CPU_SHARES has been set to 1024 because CPU shares' quota
* is commonly used in cloud frameworks like Kubernetes[1],
* AWS[2] and Mesos[3] in a similar way. They spawn containers with
* --cpu-shares option values scaled by PER_CPU_SHARES. Thus, we do
* the inverse for determining the number of possible available
* CPUs to the JVM inside a container. See JDK-8216366.
*
* [1] https://kubernetes.io/docs/concepts/configuration/manage-compute-resources-container/#meaning-of-cpu
* In particular:
* When using Docker:
* The spec.containers[].resources.requests.cpu is converted to its core value, which is potentially
* fractional, and multiplied by 1024. The greater of this number or 2 is used as the value of the
* --cpu-shares flag in the docker run command.
* [2] https://docs.aws.amazon.com/AmazonECS/latest/APIReference/API_ContainerDefinition.html
* [3] https://github.com/apache/mesos/blob/3478e344fb77d931f6122980c6e94cd3913c441d/src/docker/docker.cpp#L648
* https://github.com/apache/mesos/blob/3478e344fb77d931f6122980c6e94cd3913c441d/src/slave/containerizer/mesos/isolators/cgroups/constants.hpp#L30
*/
#define PER_CPU_SHARES 1024 #define PER_CPU_SHARES 1024
bool OSContainer::_is_initialized = false; bool OSContainer::_is_initialized = false;