[Intel-gfx] i915GM+vertical RR+FPS+OpenGL

[Jesse Barnes]

On Wed, 5 May 2010 18:14:47 -0700 (PDT)
SD <sd.domrep at yahoo.com> wrote:

> Dear All.
> 
> Sorry to disturb you again.
> When I start glxgears on Fedora 13, it tells me that application and
> suppose to be OpenGL, now synchronized to Vertical Refresh Rate
> (VRR), which in my case - laptop LCD = 60. And it also tells me that
> FPS should be ~ the same. Good. No problem with it.
> 
> But when I start it - I got only ~25FPS.
> When i start to play a movie in different window, then glxgears gives
> me really nearly 60 (58,xxx)FPS.
> 
> Question is why so. If it sync. now to VRR why I do not get 60FPS
> always? I notice that conpiz as well not really smooth and it can be
> like that because FPS = 25 and not 60.
> 
> Can someone explain me that.

If you're on 945, it could be due to what I think is a bad pipe setup.
On those chips, the vblank interrupt is delayed until after a few other
things happen, and if we program the pipes/planes/plls wrong or don't
wait the right amount of time, I think it can get stuck and you'll not
receive vblank interrupts at all.  If you're lucky, the i915 driver
will share an IRQ with some other device, which will cause it to get
called.  Since the bits are still flipping in hw, we'll emit vblank
events, but they won't correspond to when they should have occurred or
occur at the right frequency.

Jesse