Vast desktop performance degradation on GPU load

[dronus]

When there is some other GPU-load, like a demanding WebGL application, the whole desktop performance degrade vastly using Ubuntu 14.04 on an Intel GPU (HD4000).

The desktop on itselfs run smoothly on this system as long there is no other GPU load.

But if an WebGL application is rendering fullscreen with for exampke 5 fps, the desktop overall framerate seems to drop likewise. While the mouse pointer is still fast, window switiching animations AND redraw of other, non-GL applications is sluggish as hell. This still holds if the WebGL window is completely obscured.

When using metacity in contrast, the only slow thing is the WebGL application itself, anything else is running fine and with immediate response, no matter if the WebGL browser is visible or not.

I guess this is a problem with GPU scheduling. Of course, the desktop would need highest priority if the screen redraw would go below some f.p.s. otherwise. That doesn't seem to be always the case?

While some people only use OpenGL by games in fullscreen mode, more and more applications (rendering, design, WebGL, video editing) are using the GPU in an desktop environment, so this is not an issue to take easy.

It also seems animations like the window switchers are timed by frame count, so they actually take much longer if frame rate drops, which makes the bug worse too.