Brook Zhou created YARN-6870:
--------------------------------
Summary: 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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