QOpenGLWidget cpu usage is abnormal

Quiccz

I am using QOpenGLWidget and have inherited paintGL, but there is no operation within paintGL. Then, I am using a timer to call update.

class myWidget : public QOpenGLWidget
{
Q_OBJCET
public:
  myWidget();
public slots:
  void call_update();
protect:
  void initializeGL() override;
  void paintGL() override;
}

void myWidget::paintGL()
{
// do nothing
};

void myWidget::call_update()
{
  update();
}

myWidget w;
QTimer* timer = new QTimer(nullptr);
connect(timer, &QTimer::timeout, &w, &myWidget::call_update);
//timer.start(16) //  10% cpu usage
timer.start(17) // 0.5% cpu usage

i know want to use vsync. so my timer need less then 16.6, but its cpu usage is abnormal