[YARN-2768] Avoid cloning Resource in FSAppAttempt#updateDemand

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Fix Version/s: 2.8.0, 3.0.0-alpha1
• Component/s: fairscheduler
• Hadoop Flags: Reviewed
• Assignee: Hong Zhiguo
• Reporter: Hong Zhiguo
• Created: 29/Oct/14 08:52
• Updated: 30/Aug/16 01:30
• Resolved: 29/Jul/15 16:45

Description

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:

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);
        }
      }
    }
  }

The code of Resources.multiply:

public static Resource multiply(Resource lhs, double by) {
    return multiplyTo(clone(lhs), by);
}

The clone could be skipped by directly update the value of this.demand.