Symfony：kernel-> loadClassCache和多个渲染控制器

A little question about cache and render controller.

I use $kernel->loadClassCache() in my app.php, to activate the app cache. So it seems to work, my site is now very fast :).

Now I want to have a wallpaper displayer, on each refresh I want to show another wallpaper, each time. But seems impossible with the very strong cache of symfony.

To display my wallpapers, i use a render controller, like this

{{ render(controller("SiteBundle:Sidebar:sidebarWallpapers")) }}

Is it a way to never cache this render part ? Or set a very short cache time ?

Thanks!