Thanks to GTX 960, a lot of people see more value and long term in investing in GTX 970 in comparison with certain GTX 960. But the stifled performance due to a bug (or ‘bug’- depending on how you would see it) is beginning to make people think twice. Complaints kept adding up to a point where reviewers (the real ones) and users started highlighting the issue.
Like boiling water, this triggered large community discussions in known PC tech forums and Reddit. Like any large discussions, there were those with sane explanation, seemingly far-fetched stories that would put UFO conspiracy theorists to shame and the usual fanboy brigade.
For those who haven’t read the original report, many Nvidia GTX 970 users complained that they’ve noticed severe performance degrade once the VRAM consumption crosses 3.5GB. In certain scenarios depending on the in-game setting and screen resolution, 500MB- 700MB memory couldn’t be used properly. Some users also pointed out that the Vmem bandwidth is falling from 150GB/s to as low as 20GB/s. Most of the complaints were single card users as far I’ve observed. Many users found this issue to have very noticeable effect on games like Shadows of Mordor and Watch Dogs.
We also managed to find a user who recorded the glitches (using Nvidia Shadowplay) while playing Far Cry 4. Along with the glitches, you can clearly see stuttering and a temporary freezing issue.
Some called it foul play- saying that it was to make GTX 980 look good. Some said it wouldn’t make sense for Nvidia to stifle memory of all things when they could have achieved it in a much better way via the GPU core design.
Eventually, all this made Nvidia Global HQ to speak up via a press release:
The GeForce GTX 970 is equipped with 4GB of dedicated graphics memory. However the 970 has a different configuration of SMs than the 980, and fewer crossbar resources to the memory system. To optimally manage memory traffic in this configuration, we segment graphics memory into a 3.5GB section and a 0.5GB section. The GPU has higher priority access to the 3.5GB section. When a game needs less than 3.5GB of video memory per draw command then it will only access the first partition, and 3rd party applications that measure memory usage will report 3.5GB of memory in use on GTX 970, but may report more for GTX 980 if there is more memory used by other commands. When a game requires more than 3.5GB of memory then we use both segments.
We understand there have been some questions about how the GTX 970 will perform when it accesses the 0.5GB memory segment. The best way to test that is to look at game performance. Compare a GTX 980 to a 970 on a game that uses less than 3.5GB. Then turn up the settings so the game needs more than 3.5GB and compare 980 and 970 performance again.
Here’s an example of some performance data:
|GTX 980||GTX 970|
|Shadow of Mordor|
|<3.5GB setting = 2688×1512 Very High||72 FPS||60 FPS|
|>3.5GB setting = 3456×1944||55 FPS (-24%)||45 FPS (-25%)|
|<3.5GB setting = 3840×2160 2xMSAA||36 FPS||30 FPS|
|>3.5GB setting = 3840×2160 135% res||19 FPS (-47%)||15 FPS (-50%)|
|Call of Duty: Advanced Warfare|
|<3.5GB setting = 3840×2160 FSMAA T2x, Super sampling off||82 FPS||71 FPS|
|>3.5GB setting = 3840×2160 FSMAA T2x, Super sampling on||48 FPS (-41%)||40 FPS (-44%)|
On GTX 980, Shadows of Mordor drops about 24% on GTX 980 and 25% on GTX 970, a 1% difference. On Battlefield 4, the drop is 47% on GTX 980 and 50% on GTX 970, a 3% difference. On CoD: AW, the drop is 41% on GTX 980 and 44% on GTX 970, a 3% difference. As you can see, there is very little change in the performance of the GTX 970 relative to GTX 980 on these games when it is using the 0.5GB segment.
The same message was posted in Nvidia GeForce forums in an existing thread started by the users. As we can gather from what Nvidia says (some fancy fellows will use the word ‘claim’), the way SMM (Steaming Multiprocessor Maxwell) is implemented for the GM204 core is the root cause of the issue.
This could be the reason why Nvidia didn’t release GTX 960 Ti, which is supposed to use the GM 204. Nvidia would end up disabling cores (and hence the SMMs associated with each of those cores) for the GTX 960 Ti which may cause a much larger performance gap. In any which case, Nvidia’s official response does not provide a confident yes or a no. While GTX 970 still is a good card, the flaws reflecting at point of gameplay turns out to be a concern. It’s also unclear if newer drivers or GPU bios would help to fix or reduce the issue.