Low bandwidth on RTX5090 (low Core clocks and PWR limiting reason in GPU-Z)

[galkinvv]

This issue is a problem reported by @Panchovix extracted from bug about PCIe-bus related problem #57 (comment) (turned out to be a different issue)

Seems to be 5090-specific,

Currently there is a suspection that 5090 is somehow limited by VRM power, but some things are not clear yet:

• Is there a specific power rail (in hwinfo64 expanded) that is pulled high to a limit by memtest_vulkan compared to other apps like furmark. Here is a base hwinfo64 result from furmark for comparison
• Is the issue is specific to memtest_vulkan or other applications that would show High % of utilizaion of Memory Controller in GPU-Z also would suffer. For example Furmark does not give high Memory Controller utilization % (unlike 3090)

So, the following imformation from 5090 users bothered by this problem would be greatly appreciated:

1. Screenshot of up-to-date hwinfo64 while running memtest_vulkan limited by the bandwidth, with expanded sections "Gpu Power", "Gpu Performance limiters", and all memory-allocation rows visible.
2. Same screenshot while running some other app/benchmark pushing "Gpu Memory Controller Usage" at least to 60%

[xTaiwanPingLord]

I have similar issue on RTX 5070 that:

• VRAM speed is much lower on default setting, with 100% PCIe bus load.
• Even if I specify VRAM size to ~13GB, it is still lower then theoretical.

[galkinvv]

Thanks for reporting detailed info!

While running memtest_vulkan the "GPU Unknown Rail (10)" power usage for RTX 5070 is much greater compared to Furmark, while other rails have smaller power usage. It seems to be a rail corresponding to VRAM Power. And since the performance limiting reason is "power" it seems that memory power hits its limit at 80-90% GDDR7 bandwidth utilization. I'm not sure if this limit would allow utilizing 100% of gddr7 bandwith for a period longer then several milliseconds.

To be sure if the issue is specific to memtest_vulkan or the 80-90% GDDR7 bandwidth limited due to power is common for all applications - it would be useful to run some other memory-bandwith intensive workload on the 5070. Unfortunately, since ~40x0 series the classic Furmark do not impose load on the memory controller (seems that caches become bigger or drivers optimized something, so the classic Furmark is only loads the core). The MSI Kombustor tool has a memory-intensive Furmark derivative, called "Furmark-Donut (6500Mb)".
Could you try running it collecting same info via hwinfo64 screenshot?

[xTaiwanPingLord]

Sure. But I only get around 60% load on "Furmark-Donut (6500Mb)". Tried to copy memory using pytorch/cuda, but still not 100% loaded.

[galkinvv]

Thanks. So, those tools also hit power limit earlier than saturating GDDR7 bandwidth.

My hypothesis is that advertised bandwidth is achievable only for very short periods, but not for steady load that becomes capped by power limit