does cairo_paint method always slow?

Hi,
Now have two surface, one for display,another for draw.So when draw
finish, need to paint to display,
we do it this way,
cairo_surface_t * surface_display,surface_draw;
...
cairo_t *cr = cairo_create (surface_display);
cairo_set_source_surface (cr, surface_draw, 0, 0);
cairo_paint (cr);

But finally found most time was killed by cairo_paint(cr), not draw operations.
Why?Is there any better ways to do this stuff ?

Thanks,
Wei

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