CacheBasedPredictor.java

/**
 * ****************************************************************************
 * Copyright (c) 2010-2016 by Min Cai (min.cai.china@gmail.com).
 * <p>
 * This file is part of the Archimulator multicore architectural simulator.
 * <p>
 * Archimulator is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * <p>
 * Archimulator is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with Archimulator. If not, see <http://www.gnu.org/licenses/>.
 * ****************************************************************************
 */
package archimulator.uncore.cache.prediction;

import archimulator.common.SimulationObject;
import archimulator.common.report.ReportNode;
import archimulator.uncore.cache.*;
import archimulator.uncore.cache.replacement.CacheReplacementPolicyType;
import archimulator.util.ValueProvider;
import archimulator.util.math.SaturatingCounter;

/**
 * Cache based predictor.
 *
 * @param <PredictableT> the predictable type
 * @author Min Cai
 */
public class CacheBasedPredictor<PredictableT extends Comparable<PredictableT>> implements Predictor<PredictableT> {
    private EvictableCache<Boolean> cache;
    private PredictableT defaultValue;
    private long numHits;
    private long numMisses;
    private long numFailedToPredict;

    /**
     * Create an LRU cache based predictor.
     *
     * @param parent           the parent simulation object
     * @param name             the name of the cache based predictor
     * @param capacity         the capacity of the predictor
     * @param counterThreshold the threshold value of the counter
     * @param counterMaxValue  the maximum value of the counter
     * @param defaultValue     the default value
     */
    public CacheBasedPredictor(
            SimulationObject parent,
            String name,
            int capacity,
            final int counterThreshold,
            final int counterMaxValue,
            PredictableT defaultValue
    ) {
        this(parent, name, capacity, CacheReplacementPolicyType.LRU, counterThreshold, counterMaxValue, defaultValue);
    }

    /**
     * Create a cache based predictor.
     *
     * @param parent                     the parent simulation object
     * @param name                       the name of the cache based predictor
     * @param capacity                   the capacity of the predictor
     * @param cacheReplacementPolicyType the type of the cache replacement policy
     * @param counterThreshold           the threshold value of the predictor
     * @param counterMaxValue            the maximum value of the predictor
     * @param defaultValue               the default value
     */
    @SuppressWarnings("unchecked")
    public CacheBasedPredictor(
            SimulationObject parent,
            String name,
            int capacity,
            CacheReplacementPolicyType cacheReplacementPolicyType,
            final int counterThreshold,
            final int counterMaxValue,
            PredictableT defaultValue
    ) {
        this.cache = new BasicEvictableCache<>(
                parent,
                name,
                new CacheGeometry(capacity, capacity, 1),
                cacheReplacementPolicyType,
                args -> new BooleanValueProvider(counterThreshold, counterMaxValue)
        );

        this.defaultValue = defaultValue;
    }

    @SuppressWarnings("unchecked")
    @Override
    public PredictableT predict(int address) {
        CacheLine<Boolean> lineFound = this.cache.findLine(address);
        BooleanValueProvider stateProvider = lineFound != null ? (BooleanValueProvider) lineFound.getStateProvider() : null;
        if (lineFound != null && stateProvider.confidence.isTaken()) {
            return stateProvider.predictedValue;
        } else {
            this.numFailedToPredict++;
            return getDefaultValue();
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    public void update(int address, PredictableT observedValue) {
        if (this.predict(address).equals(observedValue)) {
            this.numHits++;
        } else {
            this.numMisses++;
        }

        int set = this.cache.getSet(address);
        int tag = this.cache.getTag(address);

        CacheAccess<Boolean> cacheAccess = this.cache.newAccess(null, address);

        CacheLine<Boolean> line = this.cache.getLine(set, cacheAccess.getWay());
        BooleanValueProvider stateProvider = (BooleanValueProvider) line.getStateProvider();

        if (cacheAccess.isHitInCache()) {
            if (stateProvider.predictedValue == observedValue) {
                stateProvider.confidence.update(true);
            } else {
                if (stateProvider.confidence.getValue() == 0) {
                    stateProvider.predictedValue = observedValue;
                } else {
                    stateProvider.confidence.update(false);
                }
            }

            this.cache.getReplacementPolicy().handlePromotionOnHit(null, set, cacheAccess.getWay());
        } else {
            stateProvider.state = true;
            line.setTag(tag);

            stateProvider.predictedValue = observedValue;
            stateProvider.confidence.reset();

            this.cache.getReplacementPolicy().handleInsertionOnMiss(null, set, cacheAccess.getWay());
        }
    }

    @Override
    public void dumpStats(ReportNode reportNode) {
        reportNode.getChildren().add(new ReportNode(reportNode, cache.getName()) {{
            getChildren().add(new ReportNode(this, "numHits", getNumHits() + ""));
            getChildren().add(new ReportNode(this, "numMisses", getNumMisses() + ""));
            getChildren().add(new ReportNode(this, "numAccesses", getNumAccesses() + ""));
            getChildren().add(new ReportNode(this, "hitRatio", getHitRatio() + ""));
            getChildren().add(new ReportNode(this, "coverage", getCoverage() + ""));
            getChildren().add(new ReportNode(this, "accuracy", getAccuracy() + ""));
        }});
    }

    @Override
    public PredictableT getDefaultValue() {
        return defaultValue;
    }

    @Override
    public long getNumHits() {
        return numHits;
    }

    @Override
    public long getNumMisses() {
        return numMisses;
    }

    @Override
    public long getNumFailedToPredict() {
        return numFailedToPredict;
    }

    /**
     * Boolean value predictor.
     */
    private class BooleanValueProvider implements ValueProvider<Boolean> {
        protected boolean state;
        private PredictableT predictedValue;
        private SaturatingCounter confidence;

        /**
         * Create a boolean value predictor.
         *
         * @param counterThreshold the threshold value of the counter
         * @param counterMaxValue  the maximum value of the counter
         */
        public BooleanValueProvider(int counterThreshold, int counterMaxValue) {
            this.state = false;

            this.predictedValue = null;
            this.confidence = new SaturatingCounter(0, counterThreshold, counterMaxValue, 0);
        }

        /**
         * Get the value.
         *
         * @return the value
         */
        @Override
        public Boolean get() {
            return state;
        }

        /**
         * Get the initial value.
         *
         * @return the initial value
         */
        @Override
        public Boolean getInitialValue() {
            return false;
        }

        @Override
        public String toString() {
            return String.format("{predictedValue=%s, confidence=%s}", predictedValue, confidence);
        }
    }
}