CanvasRenderingContext2D.drawImage is so slow in a clipping region

This is my code

context.save();
context.beginPath();

//loop
clearRect(x,y,width,height);
context.rect(x,y,width,height);
//loop end
context.clip();

//loop
context.drawImage(........)
//loop end

context.restore();

The drawImage method is very fast if there is no clipping area. But the fps is drop to 10% if there are clipping regions.

Any workaround?