Hey all, your friendly neighborhood GPU editor here;
So I was reading the forums and this thread caught my eye. I always have an open door policy, so please feel free to email me; you don't need to yell on the forums to get my attention.
😛
Anyhow, for Civilization V:
http://www.anandtech.com/show/4135/nvidias-geforce-gtx-560-ti-upsetting-the-250-market/9
We have always considered Civ 5 an interesting game both for its near-complete use of the DX11 feature set, and because of its interesting performance characteristics. 2 weeks ago we called it CPU limited based on the fact that once we had sufficiently powerful cards, AMD and NVIDIA results tended to clump together despite any difference in their respective cards’ speed. With the Forceware Release 265 drivers, NVIDIA has blown this assumption apart, with NVIDIA’s more powerful cards launching ahead at 1920 and lower. We appear to be quite GPU limited on the NVIDIA side all of a sudden, which is about as drastic change as we could expect. Furthermore NVIDIA is holding their cards close to their chest on this – they’ve obviously found a wonder optimization, but they aren’t ready to say what it is.
It's basically this in a nutshell. I'm not too sure what I can say that wasn't already in the article, but I'll see what I can do.
If you look at the old results, you'll notice that for single-GPU results, AMD and NV results tended to cluster together. The AMD cards would do around 32-36fps at 1920, while the NV cards would do 38-42fps or so. Obviously if we were truly CPU limited by the game, then everything would be about the same. Instead even slower NVIDIA cards do a bit better here. At the same time if we were GPU limited (even if the difference came down to specific architectural quirks), then we would see at least
some scaling with faster GPUs, which we haven't seen.
There is a 3rd option however, and it's something that doesn't come up too much: being CPU limited
by the driver. If AMD and NVIDIA are doing setup in a different manner (and they are), then you could see different results when you're CPU bound in the driver setup process. Furthermore setup can be an expensive process due to a number of reasons, so being setup limited doesn't necessarily point towards any one factor right away. Pre-tessellation vertices are probably the textbook example here, but this is probably not the case. Whatever the case, if we are driver limited, then with previous drivers it looks like AMD had more CPU overhead than NVIDIA, explaining the higher results for NVIDIA cards.
This all changed with Release 265 obviously, and now NVIDIA is much less CPU limited. Ultimately I am not sure what NVIDIA did to their drivers because they aren't willing to talk about it and let AMD see their hand. However from the data I have it's clear that something was going on with this game that created a driver bottleneck. In turn whatever that bottleneck is, NVIDIA has finally found it (keep in mind Civ 5 was released 4 months ago) and moved the bottleneck back to the GPU. If AMD has a similar bottleneck, then there's no reason to believe that they can't find it and pick up similar gains.
-Thanks
Ryan Smith
PS Keep in mind that virtually every DX11 title released up through the end of 2010 would have been developed solely against AMD cards, at least at first. AMD was sampling Juniper (5700 series) to developers in the early summer of 2009. Similar NVIDIA hardware wasn't available until a couple of months into 2010, around when the first consumer products launched.
