VSYNC makes CPU high in fullscreen ?!   

Hi,

I have a simple renderloop, which just clears the screen to black and
draws FPS in the top left corner. If I switch to fullscreen with VSYNC
on, my application starts eating 20-30% CPU for just calling a Clear
and Present. If I switch off the VSYNC, it works fine, causing 0-1%
most of the time. I'm using DXUT library, I've tried searching in the
code for anything suspicious...I couldn't find anything.

As not that experienced DirectX programmer, I ask, is there anything
other than turning on the VSYNC in the PresentParameters I should do
when using vsync, should I do any checks ?



Thanks,
George

date: Thu, 26 Jun 2008 10:05:36 -0700 (PDT)   author:   Pencheff

Re: VSYNC makes CPU high in fullscreen ?!   

I just did a search on that problem in this group, it seems that it's
a DirectX issue, so I find my workaround with putting a pre-calculated
sleep before calling Present, which doesn't guarantee that Present
will always keep up with the refreshrate, but it's still better to
drop few frames than to have excessive CPU usage.

date: Thu, 26 Jun 2008 13:43:29 -0700 (PDT)   author:   Pencheff

Re: VSYNC makes CPU high in fullscreen ?!   

On Jun 26, 1:43 pm, Pencheff  wrote:
> I just did a search on that problem in this group, it seems that it's
> a DirectX issue, so I find my workaround with putting a pre-calculated
> sleep before calling Present, which doesn't guarantee that Present
> will always keep up with the refreshrate, but it's still better to
> drop few frames than to have excessive CPU usage.

I highly recommend actually running a CPU benchmark with wait for
vsync on and off and compare the results.  Don't trust the numbers you
get from Task Manager or perfmon, as the CPU utilization can be
misleading.  I think when the CPU goes into a wait in the kernel-mode
driver the CPU utilizaiton shows as 100%, but it can still be
interrupted by other processes.

--Matt

date: Fri, 27 Jun 2008 08:44:06 -0700 (PDT)   author:   Clint Eastwood

Re: VSYNC makes CPU high in fullscreen ?!   

On Jun 27, 6:44 pm, Clint Eastwood  wrote:

> I highly recommend actually running a CPU benchmark with wait for
> vsync on and off and compare the results.  Don't trust the numbers you
> get from Task Manager or perfmon, as the CPU utilization can be
> misleading.  I think when the CPU goes into a wait in the kernel-mode
> driver the CPU utilizaiton shows as 100%, but it can still be
> interrupted by other processes.


I'm actually running a 1080p video inside using VMR9, it starts to
freeze frames when CPU usage goes above 40%, so I guess that's my
benchmark...after adding that sleep before calling present, everything
seems normal.

So, right now my renderloop (which is a separate thread from VMR9)
looks like this:

void RenderThreadProc()
{
 while( !quit )
 {
  Move();
  Render();
  if (fullscreen & vsync_on)
    sleep( calculated interval );
  Present();
 }
}

The calculated interval is being calculated when device is calculated,
the value depends on the monitor refresh rate, but commonly it's
something between 5 and 10 (which will vary on different CPUs).

Any better idea ? Is there a command to wait for vertical sync in
Direct3D (something like WaitForVerticalBlank() in DirectDraw) ?

date: Fri, 27 Jun 2008 09:22:07 -0700 (PDT)   author:   Pencheff

Re: VSYNC makes CPU high in fullscreen ?!   

> Any better idea ? Is there a command to wait for vertical sync in
> Direct3D (something like WaitForVerticalBlank() in DirectDraw) ?

Nothing explicit that I could find.  However, you can loop over
IDirect3DDevice9::GetRasterStatus() until the status indicates
that you are in the vertical blank.  This is a clunky way of doing
WaitForVerticalBlank().

kodecharlie

date: Mon, 7 Jul 2008 11:46:53 -0700 (PDT)   author:   kodecharlie