nvtop keeps otherwise-idle dGPU awake, significantly increasing system power consumption

[qwertychouskie]

As the title says, if nvtop is running, the Nvidia (or AMD) dGPU is kept powered up even if nothing is using it, which on laptops, can easily double overall idle power consumption.

See also: https://gitlab.com/mission-center-devs/mission-center/-/issues/30

[qwertychouskie]

NVIDIA/open-gpu-kernel-modules#582

[qwertychouskie]

From https://gitlab.com/mission-center-devs/mission-center/-/issues/30#note_1729912246:

It looks like lsof or fuser might be our best bet to see if applications are actually using the dGPU before calling nvidia-smi or such.

fuser -v /dev/dri/render*
fuser -v /dev/nvidia*
lsof /dev/nvidia*
lsof /dev/dri/render*

The one limitation I have found thus far is that fuser only returns processes by the current user, unless ran as root. My concern would be the potential to report "0%" usage when the usage is not actually 0%, due to some other user (or root) process using the dGPU. Invoking pkexec should make sure we are not reporting improperly when root/other users are using the dGPU, but, well, I kinda don't want to always invoke an admin prompt just to avoid an edge case. setuid on a tiny binary dedicated to this purpose is an option, but a potentially risky one.

[Syllo]

I think that I can do something really simple: close all the device handles for the GPUs that are not marked to be monitored. (you can choose which GPU to monitor through the F2 menu).
That way the GPU can go back to a deeper state of sleep.

[yump]

On my AMD RX-580, reading mem_info_vram_used seems to be safe / non-insomniacal. So you could skip AMD GPUs with very tiny (say, <8 MiB) VRAM utilization. Even vkcube uses less than that at default window size.

Having to manually toggle monitoring would be poor UX, IMHO. Most people wouldn't notice they had to do it to avoid wasting energy, and even for the ones who do it would be extremely hands-on.

[aviallon]

@Syllo just found-out about this. I remarked that my secondary RX 7900 XT was not powering-down when nvtop was running (thanks to the big white logo being powered-up), and since that card uses 40W idle… with electricity at more than 0,20 €/kWh where I live, it quickly becomes expensive.

[yump]

In the interest of having information no more clicks than necessary from the relevant Google searches, there were changes in kernel 6.13 that significantly remediated this GPU insomnia problem for some monitors (but not nvtop).

Re-testing today on 6.14.6, nvtop 3.2.0, nvtop still wakes the GPU. However grep -r . * in the GPU's hwmon sysfs directory does not. Instead it just gets a bunch of EPERM.