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https://issues.apache.org/jira/browse/YARN-2768?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Karthik Kambatla updated YARN-2768:
-----------------------------------
    Labels:   (was: BB2015-05-RFC)

> 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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