Android MPandroidchart绘图与实时不同步

我正在使用MPAndroidchart绘制实时线图。我在一秒钟内有240个值要绘制。但绘制速度太慢,绘制一秒钟的数据需要5秒以上。如何在1秒内绘制1秒数据?

private void addEntryGraph1() {
LineData data = graph1.getLineData();
if (data != null) {
    ILineDataSet set = data.getDataSetByIndex(0);
    if (set == null) {
        set = createSet();
        data.addDataSet(set);
    }
    data.addXValue(new SimpleDateFormat("HH:mm:ss")
            .format(new Date(System.currentTimeMillis())));
    for (int i = 0; i < sampleRatio; i++)
        data.addEntry(new Entry((float) (ch1Buffer.get(i)), set.getEntryCount()), 0);
    graph1.notifyDataSetChanged();
    graph1.setVisibleXRange(240, 240);
    graph1.moveViewToX(0);
    synchronized (ch1Buffer) {
        ch1Buffer.subList(0, sampleRatio).clear();
    }
}

}