UIElementUltility.dodispatch onGUi spend lots of time

Hi,

So I have a custom editor window, which can make user decide which layout they want to use , grid layout or list layout, user slide the slider to decide the layout ( like the window that come out by click the material's texture filed ) , but i find out that sometime it spend so much time on "UIElementUltility.dodispatch. onGUI" just when i slide to list layout ( profiler show it cost 99.9% of time ),

I want to know what is it doing , and how can i fix it .

Thank you.