prime render offloading, and battery life…

In my previous post I described how to get NVIDIA prime render offloading to work.

I have investigated a bit more, and found ot two things regarding this, and power usage.

  1. With prime render offloading enabled both graphics cards stay powered up all the time. Makes sense, you want to be able to use either one of them at any time, after all.
  2. Changing the setup to use suse-prime-bbswitch instead of suse-prime makes it possible to power off the nvidia card when it’s not used. That means you have to actively switch to the nvidia card, and relog, to be able to use it. You have to use sudo to do so, the plasma applet actually gets confused by the output of prime-select in this case, and doesn’t work right – it always “thinks” the nvidia card is active even when you’re using the intel card.

Finally, here’s some numbers from my laptop:

With PRIME render offloading enabled, but nothing using the NVIDIA card:
9.5W power consumption, estimated battery life 6 hours

With PRIME render offloading enabled, and glxspheres running:
13.9W, 4 hours

Without PRIME render offloading, intel card active and NVIDIA card powered down:
7.7W, 7 hours

Without PRIME render offloading, NVIDIA card active:
11.5W, 5 hours.
Looks like the intel card does not get powered down when inactive.

Note: these numbers are educated guesses at best, all I did was run powertop while operating on battery.

The battery life time is based on 56Wh, and rounded to the nearest whole number.

I didn’t measure the power consumption with glxspheres and render offloading disabled, it stands to reason that it’ll be not much different from glxspheres with offloading since the intel card is active as well in both cases.

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