System Config:-

1 HPxw9400 workstation.
2 GPUs (QuadroFX 4400G + QuadroFX 4500G)
1 G-Sync card (Primary -> 4500G & Secondary -> 4400G)
4 Monitors (2 in HorizontalSpan on 4500G & 2 in HS on 4400G)
WindowsXP + DualCore Intel CPU + 3GBRAM

From the NVIDIA Control Panel:-

The 4500G is configured as Master with internal framelock signal source. The 4400G is configured as Slave and synchronizes with the Master’s framelock signal.

Application code:-

2 OpenGL windows each one covering 1 horizontal span. So 2 (DC, RC)'s.
Enabled the 2 devices for G-Sync and checked its configuration.

Win1 -> HS1 -> 4500G -> Master -> Internal source -> Enabled
Win2 -> HS2 -> 4400G -> Slave -> External source -> Enabled

I reset the counter on the Master device. So far the setup looks fine.

When I render to the win1 & win2 and call swapbuffers on both sequentially it takes a while (about 15 sec) to display the frame and gets worse for subsequent frames. Application runs fine without G-Sync, no stall everything is smooth and real-time.

Are 4400G & 4500G compatible ? If so, is it possible to use both GPUs on the same machine as I’ve done ? Is there anything else that I’m missing in using the G-Sync ?

I don’t know anything about this.
However, I would seem more natural that the most powerful card should be the slave, as when the (slow) master finishes a frame, you can be sure that the slave have already finished its own.

You should use NV_swap_group apparently.

I’ve already tried switching the master and the slave but din’t make a difference. I’m using the swap group and swap barrier externsions. already.

if I remember correctly, there’s a 15 second time out with the nv swap group extension. So it sounds like one of your two window is waiting for the other to swap, or something.

Every other frame it takes approx. 14 sec to execute SwapBuffers of horizontal span 2. Have any idea why that is. Without G-Sync there is no such delay.

to the win1 & win2 and call swapbuffers on both sequentially

And what about calling swapbuffers in parallel ? knackered suggests that a 15 sec timeout means that one swap waits for the other to complete.