(I work for Dell) - specifically, I do a lot of optimization.
I think you're tracking a bit off course; "Above 4G decoding" is a feature left over from when BIOS PCIe memory enumeration was limited to 32bits, which is no longer the case and hasn't been for quite some time. The addressing is now native 64 bit.
But we have about 50% lower gpu performance than other servers.
I'm not sure what you mean by this. I may be reading too much into this, but this statement makes me think this may be your first foray into optimization in which case, awesome! It's a complicated but fascinating world. GPU performance can be measured in myriad different ways so this statement on its own doesn't narrow down what the problem is.
With regards to why you're seeing poor performance, this is an enormously complex question on which people write entire books. Some common mistakes I see people make particularly on AMD-based servers:
- Failing to account for PCIe lane / proc alignment. Make sure whatever processes you're running against the GPU are assigned to the proc that has the GPU's PCIe lanes rather than the distant proc
- Failing to set NUMA's per core appropriately for the workload (this is unique to AMD systems like the R7525)
- Failing to account for bottlenecks elsewhere. For example: I've had people see poor GPU performance but in reality part of their software was storage IO bound.
- Maybe this is obvious, but try setting the BIOS profile to performance. If you set it to power saver that can lead to downclocks potentially when you don't want them
- Poorly aligned memory transfers
Optimization is extremely workload specific. If this is the first time you've gone through it, I would focus my time on really understanding exactly how the data flows and where it might be bottlenecking. Try to identify things that seem out of place. Ex: if you think GPU performance is low, what is the GPUs utilization? Is it at 100%? If it is close to 100%, I start to lean towards software problems. If it's not at 100%, why is it not? Are you not feeding it data fast enough? Is the card underpowered? Server overheating? Etc.
