The HMM looks like have an accumulation delay??

[Sunnystaste]

            long start = System.currentTimeMillis();
            hmmManager.setGpsList(gpslist);
            List<Foot_Data> list = hmmManager.GetLocations();
            long end = System.currentTimeMillis();
            Log.e("HMM TIME COST", String.valueOf(end - start));

public List<Foot_Data> GetLocations() {
    setUpClass();
    ViterbiAlgorithm<RoadPosition, GpsMeasurement, RoadPath> viterbi =
            new ViterbiAlgorithm<>();
    TimeStep<RoadPosition, GpsMeasurement, RoadPath> prevTimeStep = null;
    for (GpsMeasurement gpsMeasurement : gpsList) {
        final Collection<RoadPosition> candidates = computeCandidates(gpsMeasurement);
        final TimeStep<RoadPosition, GpsMeasurement, RoadPath> timeStep =
                new TimeStep<>(gpsMeasurement, candidates);
        computeEmissionProbabilities(timeStep);
        if (prevTimeStep == null) {
            viterbi.startWithInitialObservation(timeStep.observation, timeStep.candidates,
                    timeStep.emissionLogProbabilities);
        } else {
            computeTransitionProbabilities(prevTimeStep, timeStep);
            viterbi.nextStep(timeStep.observation, timeStep.candidates,
                    timeStep.emissionLogProbabilities, timeStep.transitionLogProbabilities,
                    timeStep.roadPaths);
        }
        prevTimeStep = timeStep;
    }
    List<Foot_Data> list = new ArrayList<>();
    List<SequenceState<RoadPosition, GpsMeasurement, RoadPath>> roadPositions =
            viterbi.computeMostLikelySequence();
    for (SequenceState<RoadPosition, GpsMeasurement, RoadPath> s : roadPositions){
        Point p = s.state.position;
        Road_Data road_data = s.state.road_data;
        list.add(new Foot_Data(p,road_data));
    }
    return list;
}

The GetLocations is an method to achieve map-matching algorithm. It works well,but we have find something wrong with the TIME COST,HMM looks like have an accumulation delay. Could you please tell me why the TIME COST will increase? And if I want to resolve this problem, what should I do? THK U