Secondary GPU sleeping

[danwood82]

Hey all,
Apologies if this isn't quite a home-server topic, but I generally trust getting solid technical information borne of experience over here, instead of the typical "just enough knowledge to be dangerous" responses over on Reddit and the like .

I'm considering leaving an RTX 3090 in the 3.0x4-wired secondary slot of my motherboard, to use solely for additional raytracing horsepower in Octane Render (which has pretty much linear scaling with multiple GPUs)... and otherwise use only a new RTX 4090 for everything else. This is using Windows 10.

Give than the 3090 will be idling a lot of the time (potentially for weeks/months between projects), and would never have a display connected, would it naturally go into a low-power state, or is there a specific way I can manually set it into some kind of "standby" state, short of physically pulling the card when I'm not using it?

 

[idle_user]

GPUs don't constantly stay at their rated power rate. If you're not using it, it won't draw much power and remain idle.

You can get a meter and check the consumption difference if you'd like the reassurance.

There's probably some official software out there that you can tune down the speeds too, but then you'll have to remember to reset it before starting up projects that will utilize the card.

 

[rtech]

Look at reviews that measure idle power consumption. GPU will go into low power consumption even when they are used for desktop duties.

If you want to tamper with GPU power use MSI afterburner
I use similar setup but with much less powerful GPU and on Linux the card is idle most of the time and consumes few watts.

 

[piranha32]

If you want to tamper with GPU power use MSI afterburner
I use similar setup but with much less powerful GPU and on Linux the card is idle most of the time and consumes few watts.

What do you use for power tuning on Linux? The only tool I know for tweaking clock and power settings for nvidia on Linux is nvidia-smi

 

[rtech]

What do you use for power tuning on Linux? The only tool I know for tweaking clock and power settings for nvidia on Linux is nvidia-smi

I am using it for GPU passthrough with vfio which unlike pci-stub this allowes for deeper states for GPU. I know because its fan is off when idle.
I dont use any tool as it is passthrough to Windows VM and then windows takes over

 

[danwood82]

Cheers everyone.
Yeah, I know modern GPUs typically handle their own power management fairly effectively. Was just wondering if there was a way to explicitly force the card into a fully "parked" state, so it was off-until-needed, rather than leaving it to do its own power management.

...but then, as far as I can see, the idle power usage on these cards seems to be tied fairly directly to connected monitor outputs... so hopefully just leaving it fully-headless will let it run fully-idle. It's currently my main card until I get the new one - interestingly, if I simply switch off my monitor, idle usage in Afterburner drops from 31W to 18W, and core clock drops from 210MHz to "0"MHz, with tiny activity spikes back to 210MHz every few seconds.
18W still seems a bit much to just have something sitting there doing nothing, but it's not too bad I suppose, and perhaps it might even drop lower with no background processes using it.

 

[danwood82]

Well, with it set up and running, the secondary 3090 idles along at 16-17W as expected. It'd be nice if there was an easy way to check power draw when the card is "disabled" in the device managed... I don't imagine it'll be any different - I presume that'd just mean it would fall back to firmware-level control until it's re-enabled.
Overall, not ideal, but not too bad. I've set up profiles to voltage-limit both cards when rendering to the point where they draw less together than the max power limit of just the 4090 alone, and they still run over 95% of default peak performance. A nice chunk of raytracing power - the 3090 was fast, but now it's suddenly like I have three of them in there

 

[Stankyjawnz]

You should check in your OS if ASPM is enabled. I believe you can see in windows device manager or in Linux using lspci -vv. If ASPM is enabled you may be able to achieve lower idle power on that card. You may need to turn on ASPM settings in bios.

 

[rtech]

FYI on Linux you can also toggle power settings with powertop but i would not recommend it. All hw ive tried it on started to act weird or unstable.
Server hw is built to be efficient at load not to be idle.

 

[danwood82]

You should check in your OS if ASPM is enabled. I believe you can see in windows device manager or in Linux using lspci -vv. If ASPM is enabled you may be able to achieve lower idle power on that card. You may need to turn on ASPM settings in bios.

Good shout, I found the BIOS setting, which was already "Auto", but tried "Enabled"... also tried dropping the Windows power profile back to "Balanced" and "Power Saver" which allow Link State Power Management. Alas, it doesn't seem to let the card drop into any lower power state than the standard idle mode that's clocking 16-17W. Under Device Manager>Details>Power Data, it seems to suggest that the card supports a "D3" power state, but as it stands, it never shifts out of "D0" state.