GTX 980 Ti for Mac Pro 4,1 recommendations

[iAssimilated]

I am now all in! I have read most everything Jay has posted on THE HOUSE OF MOTH regarding the Pixlas Mod. I am currently buying the parts for the mod as well as the Powerlink. The situation is easy for me because the Mac Pro was free, so all the other costs associated to this I view as the price I would pay towards a Mac Pro anyways. I admit, I really really really want to go the easy route, but since I will be installing linux on the system I don't trust the OS will protect against the possibility of frying the backplane and I don't have an infinite supply of free Mac Pros.

Interesting times ahead!

 

[webbp]

I can confirm that editing the 980 Ti BIOS to limit max power to 75W from each PCIe power socket does successfully limit the power draw without compromising performance all that much. (Slot power was already set to max 75W in the stock BIOS.) However, I don't know for sure whether or not running software like MSI Afterburner or some Linux equivalent could accidentally increase the max power to unsafe levels while it is running, so I'm being careful not to run any software that soft-modifies GPU settings. I can provide more information on how to do this on request.

Update: I confirmed that the BIOS-limited power consumption also works in Linux. More specifically, I booted to Ubuntu 21.04, set performance to maximum in NVIDIA control panel, ran GpuTest furmark 1080p, and observed with nvidia-smi that that the 980 Ti's power consumption remained below the maximum I had set in its BIOS.

 

[macguru9999]

why would you want to risk damaging a perfectly good mac pro and install a card that is not compatible with mojave or catalina ? it makes no sense.... get a radeon rx480/580 , flashed or otherwise. If you must use a card that draws more power, do the pixlas mod. changing backplane boards is expensive.

 

[webbp]

why would you want to risk damaging a perfectly good mac pro and install a card that is not compatible with mojave or catalina ? it makes no sense.... get a radeon rx480/580 , flashed or otherwise. If you must use a card that draws more power, do the pixlas mod. changing backplane boards is expensive.

I do machine learning, and most GPU-accelerated machine learning requires an NVIDIA GPU. I use 10.13.6 because the 980 Ti still works. There are two Mojave / Catalina features which interest me: dark mode and Xcode 11+.

I have an RX 580 and have succeeded in using it with Vulkan via MagmaVK for some machine learning tests, but Vulkan is not nearly as well-supported as CUDA for machine learning, and the latest MagmaMK requires Xcode 11+ to build. Therefore, I plan to install Mojave on another drive to test that setup and follow the progress of macOS + AMD GPU + Vulkan for machine learning in pytorch and julia flux.

I do plan to do pixla's mod, but until the parts arrive, for the purpose of using a Mac Pro 4,1/5,1 for machine learning, a 980 Ti with BIOS-limited power consumption makes sense. A 1080 Ti is also a good choice, but more expensive.

If you have a better alternative, I'm all ears!

 

[iAssimilated]

All the parts finally arrived today so I was able to do the Pixlas Mod this evening on my 5,1 MacPro. The whole thing took about an hour and a half. When I installed the taps I got a bit too close with a couple of them so I decided to ditch my entire optical drive bay (I did not want to pinch the cables by re-installing it and I have multiple USB DVD-RW drives). I had to route the new power cable behind and slightly below the PCI fan because I am also using the EVGA Powerlink. I was unable to plugin the power cable to my 980 Ti with the Powerlink attached.

I had installed KDE neon earlier while using an old AMD HD 5770. With the Pixlas Mod and the 980 Ti the Mac Pro and OS booted up just fine. I am currently trying to get Steam to work, but I'm having an issue even though the proprietary nvidia drivers are installed. Starting to realize why it was so easy to leave linux behind. On to the next challenge I suppose.

 

[KeesMacPro]

I had to route the new power cable behind and slightly below the PCI fan because I am also using the EVGA Powerlink. I was unable to plugin the power cable to my 980 Ti with the Powerlink attached.

It's not necessary to use the EVGA Powerlink in combination with a Pixlas Mod.
Better said: it doesnt make sense.

The 6/8 pin power connectors are directly connected to each other , so there is nothing to equalize between them.

 

[iAssimilated]

It's not necessary to use the EVGA Powerlink in combination with a Pixlas Mod.
Better said: it doesnt make sense.

The 6/8 pin power connectors are directly connected to each other , so there is nothing to equalize between them.

Good to know... thanks! Although, I am done fiddling with the hardware of this box at the moment. I need to resolve my software issues before I'll be motivated to take things apart. I installed the Powerlink as well simply because I had it (no sense in wasting money).

 

[h9826790]

It's not necessary to use the EVGA Powerlink in combination with a Pixlas Mod.
Better said: it doesnt make sense.

The 6/8 pin power connectors are directly connected to each other , so there is nothing to equalize between them.

IMO, Yes and No.

PowerLink has few functions, the two main functions are balancing the power draw and smooth out the power spike.

There is no reason to balance the power draw after Pixlas mod. However, the power spike still there. Even there is no real need to smooth that out. But "if the user already has PowerLink on hand", then it's nothing wrong to use it as "current regulator" in the circuit.

But if that greatly increase cable management's difficulty. I will also skip the PowerLink.

 

[KeesMacPro]

IMO, Yes and No.

PowerLink has few functions, the two main functions are balancing the power draw and smooth out the power spike.

There is no reason to balance the power draw after Pixlas mod. However, the power spike still there. Even there is no real need to smooth that out. But "if the user already has PowerLink on hand", then it's nothing wrong to use it as "current regulator" in the circuit.

But if that greatly increase cable management's difficulty. I will also skip the PowerLink.

You got a point about buffering the spikes.

TBH i thought about that too, but to have that effect, there's quite a capacity needed, since there's a high current running.
Looking at the size of the powerlink , i doubt a big capacitor/ a lot of small capacitors will physically fit...

So I think this smoothing effect is marginal.
To find the answer I could buy one and open it

 

[h9826790]

You got a point about buffering the spikes.

TBH i thought about that too, but to have that effect, there's quite a capacity needed, since there's a high current running.
Looking at the size of the powerlink , i doubt a big capacitor/ a lot of small capacitors will physically fit...

So I think this smoothing effect is marginal.
To find the answer I could buy one and open it

Someone posted the inside of a PowerLink before. You may search for that post.

Anyway, from memory, there are two small capacitors inside the PowerLink.

I don't know how effective they are. However, back into the days that "1080Ti can shutdown the cMP when running CUDA-Z heavy test" (due to power spike, even with power balancing by using cables combination). A PowerLink can avoid this very effectively.

So, even though the caps aren't big enough to completely smooth out the current. But it seems that's good enough to avoid excessive power spike. And actually able to avoid the hard shutdown protection in some cases.

 

[iAssimilated]

You got a point about buffering the spikes.

TBH i thought about that too, but to have that effect, there's quite a capacity needed, since there's a high current running.
Looking at the size of the powerlink , i doubt a big capacitor/ a lot of small capacitors will physically fit...

So I think this smoothing effect is marginal.
To find the answer I could buy one and open it

From their product page:

The only benefit I see at the moment with removing the Powerlink is the PCI fan will blow more air directly on the rear of the GPU's heatsink .

 

[KeesMacPro]

From their product page:

The only benefit I see at the moment with removing the Powerlink is the PCI fan will blow more air directly on the rear of the GPU's heatsink .

Thx for the info , I appreciate it!

 

[webbp]

Update on flashing 980 ti rom to limit power vs pixla's mod

My parts arrived, and I performed pixla's mod and flashed my 980 ti back to stock rom.

Benchmarks
power limited rom: furmark 4k fullscreen avg fps: 26
stock rom: furmark 4k fullscreen avg fps: 36

Power draw was 250W max with stock rom + pixla's mod vs 200W max with power limited rom (limited to 75W slot power and 75W for each power socket). Oddly, power draw never exceeded 200W with the power limited rom, even though 75W * 3 = 225W. Performance increased by ~40% with stock vs power limited rom. Creating a custom overclocked rom is now also an option, and would further increase performance. However, heat and noise were already much increased with the stock rom. Presumably the increased power draw and heat caused by using the stock rom or an overclocked rom may decrease the lifespan of the GPU and the Mac Pro's PSU and other components.

Overall, I think doing pixla's mod for the first time was easier and less time-consuming than flashing a GPU for the first time. I'm not very experienced with Windows, information is scattered and conflicting, e.g., about which version of nvflash to use, etc... However, for the 2nd..nth time, now that everything is set up, flashing is easier.

I am very happy I did pixla's mod because (a) the backplane's pcie power sockets are now available to other cards, e.g. usb3, thunderbolt, (b) i got a 40% gpu performance increase, and (c) it was enjoyable and satisfying.