tl;dr - If I attach a second monitor to my laptop showing the same as its integrated display at the same resolution / refresh rate, I would have thought that logically that shouldn’t require the GPU / CPU to do any additional work. It’s the same signal just being fed to two places. But experience of the last few years running a second display attached to a dock suggests that the laptop has to do a lot more work to drive this second display, resulting in excess heat and fan noise compared to when using the laptop undocked. Why is this the case, and is there a way to avoid it?
Additional blurb:
I’ve found the laptop + dock concept to be my perfect setup, but my 11-year-old Dell D630 laptop is really labouring. It spends most of its life docked with its highest resolution output mirrored to a larger TV-monitor at 1280x800 / 30fps. This particular laptop model was known for heat issues but when it conked out I located one of the later generation motherboards that isn’t prone to the same failure. It runs very hot and I sometimes (but mysteriously, not always) get very stuttering video over my fibre broadband from YouTube and other sites, seemingly because the CPU thermal sensor forces a temporary speed drop-down. But I’m not sure, this could also be my French Internet provider who is known for deliberately limiting bandwidth on YouTube and other sites all as part of political gaming.
Anyway, whilst the laptop still serves me well generally in 2018, these video issues make me wonder about getting something more up-to-date, but I can’t afford a new laptop. And most secondhand laptops for a good price are still 1366x768. My TV-monitor can handle full HD 1920x1080 and I’d like to get a laptop that can output that as native, but my concern is that unless it’s something very recent and hence unaffordable, it will strain in just the same way to output to two screens in full HD. And so maybe I should just plod on for another year and try to save up for a better device. Thoughts?
Edit: some additional specs:
openSUSE Leap 42.3 running Plasma 5.8.7
2 x Intel Core 2 Duo T7700 @ 2400MHz
nVidia Quadro NVS 135M
Wanted to add that I can watch local videos full screen at 1280x800 no problem. Whilst that suggests an Internet bandwidth issue it could also be the stream decoding that causes CPU/GPU overhead.
And some more specs:
4GB RAM + 4GB swap
There is usually spare RAM available and very little swap usage.
I would expect that your observation about GPU load is because you <can> mirror or clone your displays with same resolution, that doesn’t necessarily have to be configured that way.
In fact,
If your displays are very different, you’d want to be able to custom configure the output to each display to optimally display generally according to the defaults of each display.
I’m not sure I catch your drift (wow, that sounds such an 80s expression) with the first sentence.
As for configuring the displays optimally, I don’t know if you mean independently? The optimal (native, default) resolution of my TV-monitor is 1920x1280, but my laptop cannot output at higher than its own native resolution of 1280x800, and I wouldn’t want to have a different resolution on one screen anyway. I run most of my apps maximized. Everything is set up to be optimal in the sense of configured column widths and so on, so if I then undock the laptop and have to revert to using a lower resolution on its integrated screen, it screws everything up.
But you might have rather been implying just getting the other settings optimized. As far as I know they are already, although the control over that isn’t ideal. In the default Plasma that comes with Leap 42.3, under the display settings, there is a ‘Unify Outputs’ button. I press that and presume that it’s mirrored everything automatically to the best setting on each screen. I know that my TV-monitor should do 60fps no problems according to its manual, but if I try to set that manually, when I next enter the display settings it has always reverted to 30fps.
But the thing I’m most keen to know is the basic theory behind mirroring a display - whether it should entail additional CPU/GPU load or not. Does it depend on the type of output (HDMI, DisplayPort, VGA, etc.)? In this case my second monitor is attached via VGA. The only other option this laptop and dock offers is S-video. I would have just thought that logically you could mirror to 1,000 screens and not cause any overhead on the laptop, because it’s only outputting the signal once. And if that’s not the case, how come?
I never mentioned before that this is all when running with the nvidia proprietary driver. I’ve done 3 new installs on this machine, the most recent being Leap 42.2, and all initially defaulted to nouveau, and on each occasion it barely lasted five minutes before crashety-crash-crash all over the place. So that’s not really an option.
