GTX 970 memory bug reportedly cripples performance in memory intensive scenarios
- By Joel Hruska on January 23, 2015 at 6:18 pm
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Ever since the GTX 970 and GTX 980 launched, I’ve made no secret of preferring the GTX 970 as a gaming solution for the vast majority of people. For $200 less, this GPU seemed to pack nearly all the benefits of Nvidia’s Maxwell, with very little downside — until now. Now, reports are surfacing that the GTX 970 may suffer from a serious memory bug that may cripple performance in certain scenarios.
In order to explain things, I need to first cover how GPU memory access is supposed to work. One of the reasons of building a large ring bus and multiple memory controllers around the outside of the die is that memory accesses to every block of RAM are supposed to have the same latencies and take the same amount of time. Accessing the first 500MB of GPU VRAM shouldn’t be faster or slower than accessing the last 500MB.
Unfortunately, that’s not what the GTX 970 is doing, as evidenced by benchmark results like the below. What follows is a simple RAM bandwidth test of both the DRAM and the L2 cache on the GTX 970 (left) and the GTX 980 (right).
Note that performance is constant between both cards until you hit the end of the memory pool in both cases. When the GTX 970 hits the 3.2GiB mark, performance craters, falling to less than 20% of its initial rating in some cases. The GTX 980, in contrast, maintains full bandwidth across the entire GPU — 178GB/s for DRAM and 554GB/s for L2 cache.
Does this have a real-world impact?
We’re going to be conducting some tests of our own, but preliminary data says it does. Reports of games stuttering above the 3GB mark are common on the GeForce forums; the thread has currently reached some 20 pages. This should be fairly easy to test — the GTX 970 and GTX 980 have the same amount of memory and the same bus width.
If the GTX 970’s performance drops or begins stuttering dramatically above 3GB, as many users are reporting, it’ll be evidence that the problem is real. Nvidia has said only that they’re looking into the problem and will provide an update as soon as possible.
This could be a major issue given that 4K monitors are shipping in greater volume while the latest console games tend to use far more VRAM than previous models. If hardware tests show this problem is significant, hopefully Nvidia can resolve it. If not, a number of buyers are going to be exceptionally unhappy. If you have a GTX 970, please feel free to get in touch with me or sound off in the comments if you’ve noticed unusual stuttering or performance degradation at high resolution. If you’re wondering how to check real-time memory usage, the freeware program GPU-Z provides one method of logging that data.
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