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Posted to yarn-issues@hadoop.apache.org by "Arun Suresh (JIRA)" <ji...@apache.org> on 2017/07/25 21:09:00 UTC
[jira] [Updated] (YARN-6870)
ResourceUtilization/ContainersMonitorImpl is calculating CPU utilization as
a float, which is imprecise
[ https://issues.apache.org/jira/browse/YARN-6870?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Arun Suresh updated YARN-6870:
------------------------------
Target Version/s: 2.9.0, 3.0.0-beta1
> ResourceUtilization/ContainersMonitorImpl is calculating CPU utilization as a float, which is imprecise
> -------------------------------------------------------------------------------------------------------
>
> Key: YARN-6870
> URL: https://issues.apache.org/jira/browse/YARN-6870
> Project: Hadoop YARN
> Issue Type: Bug
> Components: api, nodemanager
> Reporter: Brook Zhou
> Assignee: Brook Zhou
>
> We have seen issues on our clusters where the current way of computing CPU usage is having float-arithmetic inaccuracies (the bug is still there in trunk)
> Simple program to illustrate:
> {code:title=Bar.java|borderStyle=solid}
> public static void main(String[] args) throws Exception {
> float result = 0.0f;
> for (int i = 0; i < 7; i++) {
> if (i == 6) {
> result += (float) 4 / (float)18;
> } else {
> result += (float) 2 / (float)18;
> }
> }
> for (int i = 0; i < 7; i++) {
> if (i == 6) {
> result -= (float) 4 / (float)18;
> } else {
> result -= (float) 2 / (float)18;
> }
> }
> System.out.println(result);
> }
> {code}
> // Printed
> 4.4703484E-8
> 2017-04-12 05:43:24,014 INFO org.apache.hadoop.yarn.server.nodemanager.containermanager.monitor.ContainersMonitorImpl: Not enough cpu for [container_e3295_1491978508342_0467_01_000030], Current CPU Allocation: [0.8888891], Requested CPU Allocation: [0.11111111]
> There are a few places with this issue:
> 1. ResourceUtilization.java - set/getCPU both use float. When ContainerScheduler calls ContainersMonitor.increase/decreaseResourceUtilization, this may lead to issues.
> 2. AllocationBasedResourceUtilizationTracker.java - hasResourcesAvailable uses float as well for CPU computation.
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