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benmuetsch

macrumors member
Original poster
Oct 10, 2020
94
39
Hi everyone,

I've just gotten my hands on a reference Vega 56 card which I planned on installing into my MacPro5,1 running Catalina w/ MartinLO OC package.
I'm using this computer for music production and soundtracks so I basically don't really need the raw horsepower of the card, but would like to have HWaccel for h264 and hevc, which my old nVidia GTX card (GTX 650) doesn't provide.
My concern with AMD cards always has been the high idle power draw with two or three monitors connected, which is not a problem with the GTX at all. After investigating, the Vegas have been reported to behave better in this regard due to HBM2 memory.
I've installed the card for testing the last days only with dual mini-6pin to 8pin cables, which is not ideal, I know, but the first power draw numbers seemed promising according to iStat menues.

The thing now is: after the machine boots up, istat menues reports a low p0-state for the GPU, but the HBM2 memory directly ramps up to 500Mhz and stays there. Also, if the GPU once set under slight load, the memory ramps up to 800MHz and stays there in idle, resulting in 3.5amps idle power draw in total. Interestingly, if I watch a h264 video, the memory sets back to 500Mhz just to ramp up back to 800MHz when idling again, so the card uses *less* power while watching video then in idle sitting just at the desktop.

Are the macOS drivers really that bad? On windows machines, the p0-state for Memory is around 160MHz and therefore, the power draw much lower. Is there anything I can do? I discovered a tool called VGTab, where custom powerplay tables can be injected, but I read different opinions on the tool and if it really affects clocks and voltages on macOS, or just the fans.

If there's nothing to to, I really give up on AMD and the MacPro, but that's just insane and annoying. Apple ditched nVidia long ago but the drivers are much better apparently, even with my old MacPro3,1 - when the stock 8800GT died - I put in an HD4870 if I remeber correctly - and the thing turned into a space heater. Nothing different now with the 5,1. GTX 650 / 680 and the whole computer stays cool in idle and on low intensity tasks, where with AMD cards (tested RX 470 and now the Vega 56) the thing gets warm, even the PSU puts out considerably more heat.
I would put in an RX560, but even those have been reported to draw 30W+ in idle with two different monitors connected, which is basically 1/2 of the TDP, that's just insane and dumb.

So: can I somehow manipulate the Vega to utilize more of the low power states and could I even undervolt / underclock the card? I am using the "eco-bios" on the card btw, slider set to the fan direction.

Thanks in advance for any opinions!
 
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