统计设备总内存使用率的时候为什么不用top而选择dumpsys meminfo about mobileperf HOT 1 OPEN

 /*
     * Stops tracking memory usage, binder transactions, and real & cpu timing.
     * Stores collected data as type long into Bundle object for reporting.
     */
    private void endPerformanceSnapshot() {
        // Stop the timing. This must be done first before any other counting is
        // stopped.
        mSnapshotCpuTime = Process.getElapsedCpuTime() - mSnapshotCpuTime;
        mSnapshotExecTime = SystemClock.uptimeMillis() - mSnapshotExecTime;

        stopAllocCounting();

        long nativeMax = Debug.getNativeHeapSize() / 1024;
        long nativeAllocated = Debug.getNativeHeapAllocatedSize() / 1024;
        long nativeFree = Debug.getNativeHeapFreeSize() / 1024;

        Debug.MemoryInfo memInfo = new Debug.MemoryInfo();
        Debug.getMemoryInfo(memInfo);

        Runtime runtime = Runtime.getRuntime();

        long dalvikMax = runtime.totalMemory() / 1024;
        long dalvikFree = runtime.freeMemory() / 1024;
        long dalvikAllocated = dalvikMax - dalvikFree;

        // Add final binder counts
        Bundle binderCounts = getBinderCounts();
        for (String key : binderCounts.keySet()) {
            mPerfSnapshot.putLong(key, binderCounts.getLong(key));
        }

        // Add alloc counts
        Bundle allocCounts = getAllocCounts();
        for (String key : allocCounts.keySet()) {
            mPerfSnapshot.putLong(key, allocCounts.getLong(key));
        }

        mPerfSnapshot.putLong(METRIC_KEY_EXECUTION_TIME, mSnapshotExecTime);
        mPerfSnapshot.putLong(METRIC_KEY_CPU_TIME, mSnapshotCpuTime);

        mPerfSnapshot.putLong(METRIC_KEY_NATIVE_SIZE, nativeMax);
        mPerfSnapshot.putLong(METRIC_KEY_NATIVE_ALLOCATED, nativeAllocated);
        mPerfSnapshot.putLong(METRIC_KEY_NATIVE_FREE, nativeFree);
        mPerfSnapshot.putLong(METRIC_KEY_NATIVE_PSS, memInfo.nativePss);
        mPerfSnapshot.putLong(METRIC_KEY_NATIVE_PRIVATE_DIRTY, memInfo.nativePrivateDirty);
        mPerfSnapshot.putLong(METRIC_KEY_NATIVE_SHARED_DIRTY, memInfo.nativeSharedDirty);

        mPerfSnapshot.putLong(METRIC_KEY_JAVA_SIZE, dalvikMax);
        mPerfSnapshot.putLong(METRIC_KEY_JAVA_ALLOCATED, dalvikAllocated);
        mPerfSnapshot.putLong(METRIC_KEY_JAVA_FREE, dalvikFree);
        mPerfSnapshot.putLong(METRIC_KEY_JAVA_PSS, memInfo.dalvikPss);
        mPerfSnapshot.putLong(METRIC_KEY_JAVA_PRIVATE_DIRTY, memInfo.dalvikPrivateDirty);
        mPerfSnapshot.putLong(METRIC_KEY_JAVA_SHARED_DIRTY, memInfo.dalvikSharedDirty);

        mPerfSnapshot.putLong(METRIC_KEY_OTHER_PSS, memInfo.otherPss);
        mPerfSnapshot.putLong(METRIC_KEY_OTHER_PRIVATE_DIRTY, memInfo.otherPrivateDirty);
        mPerfSnapshot.putLong(METRIC_KEY_OTHER_SHARED_DIRTY, memInfo.otherSharedDirty);
    }