How to optimize QPainter::drawPolyline()

Question

I have a QQuickPaintedItem's children class that may draw a large polylines (>100k points). The following method is used in QQuickPaintedItem::paint():

// the method being called in QQuickPaintedItem::paint()
void Plotter::drawCurves(QPainter *painter) 
{
    // ...

    QLinkedList<QPointF> data = iterator.value();

    QPolygonF polyline(data.count());
    QPointF point;
    int i = 0;

    foreach (point, data)
        polyline[i++] = transformToCoord(point);

    QTime timer;
    timer.start();
    painter->drawPolyline(polyline);
    qDebug() << timer.elapsed();
}

void Plotter::paint(QPainter *painter)
{
    // ...
    drawCurves(painter);
    // ...
}

Painting of 100k points with QPainter::drawPolyline() takes about 120-170 milliseconds. Method QQuickPaintedItem::update() calls very often so drawing a polyline reduces program perfomance a lot.

Is there a way to speed up QPainter::drawPolyline()?