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https://issues.apache.org/jira/browse/YARN-2768?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14535590#comment-14535590
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Karthik Kambatla commented on YARN-2768:
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Thanks for working on this, [~zhiguohong].
I would like to understand this better. Looking at your profiling output, I see
that {{Resources.createResource}} under {{Resources.multiply}} takes about 61
seconds. However, the same call right *after* {{Resources.multiply}} takes 37
milliseconds. The earlier 61 seconds is likely the effect of waiting for GC.
Can you repeat this profile a few times so we understand what exactly is going
on? Also, it would be nice if we could get the GC stats around the same time.
> optimize FSAppAttempt.updateDemand by avoid clone of Resource which takes 85%
> of computing time of update thread
> ----------------------------------------------------------------------------------------------------------------
>
> Key: YARN-2768
> URL: https://issues.apache.org/jira/browse/YARN-2768
> Project: Hadoop YARN
> Issue Type: Improvement
> Components: fairscheduler
> Reporter: Hong Zhiguo
> Assignee: Hong Zhiguo
> Priority: Minor
> Attachments: YARN-2768.patch, profiling_FairScheduler_update.png
>
>
> See the attached picture of profiling result. The clone of Resource object
> within Resources.multiply() takes up **85%** (19.2 / 22.6) CPU time of the
> function FairScheduler.update().
> The code of FSAppAttempt.updateDemand:
> {code}
> public void updateDemand() {
> demand = Resources.createResource(0);
> // Demand is current consumption plus outstanding requests
> Resources.addTo(demand, app.getCurrentConsumption());
> // Add up outstanding resource requests
> synchronized (app) {
> for (Priority p : app.getPriorities()) {
> for (ResourceRequest r : app.getResourceRequests(p).values()) {
> Resource total = Resources.multiply(r.getCapability(),
> r.getNumContainers());
> Resources.addTo(demand, total);
> }
> }
> }
> }
> {code}
> The code of Resources.multiply:
> {code}
> public static Resource multiply(Resource lhs, double by) {
> return multiplyTo(clone(lhs), by);
> }
> {code}
> The clone could be skipped by directly update the value of this.demand.
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