undefined | Better HN

0 pointsepcoa1y ago0 comments

> The issue is that you keep the power-hungry shader units on, whereas when truly idle their power is cut.

Even in the most perverse scenario of a single cell update the load for a terminal is still bursty enough that it's not like the GPU doesn't enter some power saving states. Running intel_gpu_top in kytty with a 100ms update is at least suggestive, it never drops below 90% RC6 (even at 50ms, which is a completely uselessly fast update rate we're still in the high 80s). If you're updating faster than 100ms legitimately, it's probably video or animation that is updating a large percentage of the display area anyway. The overall time my terminal is doing some animation while on battery is low enough that in practice it just doesn't matter.

https://en.wikipedia.org/wiki/Amdahl%27s_law

The problem you're up against is that, maybe if this was optimized most people would get 2 or 3 (or even 10) more minutes on a 12 hour battery life or something. No one really cares. Maybe they should, but they don't. And there's plenty of other suck in their power budget.

You make it sound like a binary power saving scenario, but it tends to be more nuanced in practice.

Most people run their terminal opaque, most display systems optimize this common case.

> Also, if you do damage tracking, make sure to report it to the display server

I'm not unsympathetic to your point of view. But I am skeptical that the power savings for most use cases ends up being much of a big deal in practice for most people (even accepting there may be some annoying edge cases that annoy some). I am interested in this topic, but I am still awaiting an example of a GPU accelerated terminal emulator that works this way to even make a real world comparison.

0 comments

arghwhat1y ago

It is very nuanced, but it's important to realize how small the power budget is and how just tens of milliwatt here and there make a huge difference.

To get over 12 hours of battery life out of a 60 Wh battery - which isn't impressive nowadays with laptops rocking 20+ hours - you need to stay below 5 watts of battery draw on average, and considering that the machine will likely do some actual computation occasionally, you'll need to idle closer to 2-3 watts at the battery including the monitor and any conversion losses.

The really big gains in battery life are from cutting tens to hundreds of mW off things at the bottom by keeping hardware off and using fixed function hardware like e.g. avoiding rendering and doing direct scanout and using partial panel self refresh. Execution units do not turn on and off instantly so pinging them even briefly is bad, and the entire system needs to be aligned with the goal of only using them when necessary for them to stay off.

Efforts like libliftoff to do efficient plane offload to avoid render steps in the display server can save in the area of half a watt or more, but it's not a whole lot of help if applications don't do their part.

Bigger GPUs than your iGPU (or even just later iGPUs) will also likely see even bigger impacts, as their bigger shader units are likely much hungrier.

(As an aside, I am not a fan of kitty - they have really weird frame management and terrible recommendations on their wiki. Foot, alacritty or if ghostty turns out good, maybe even that would be better suggestions. Note that comparing to foot can give a wrong image, as CPU-based rendering pushes work to the display server and gives the illusion of being faster and more efficient than it really is.)

epcoaOP1y ago

Well I would be very interested in some of this, but it all seems theoretical and mythical. Seriously, what terminal is giving 20% better battery life (or whatever number that people will notice) than kitty.

How can I observe any of these claims in practice? You’ve put some down some bold claims about how things should be done but no way to verify or validate them at all. Put up with some real power benchmarks or this is just crack pot.

> To get over 12 hours of battery life out of a 60 Wh battery - which isn't impressive nowadays with laptops rocking 20+ hours

I used 12 hours to be nice. The sell of getting another 10 minutes or so out of 20 hours is even more stark.

The cases where you push a line and scroll, you're repainting most of it anyway. The cases where you're not are end up being infrequent enough that optimizing them in the ways suggested makes an unnoticeable impact. Build it and they will come maybe?

> Bigger GPUs than your iGPU (or even just later iGPUs) will also likely see even bigger impacts.

In most cases people can get by with an iGPU for a battery laptop cases. If you're in a must pull down more graphical power case, you're often plugged in and few care about 10s of milliwatts then.

> (As an aside, I am not a fan of kitty - they have really weird frame management and terrible recommendations on their wiki. Foot, alacritty or if ghostty turns out good, maybe even that would be better suggestions. Note that comparing to foot can give a wrong image, as CPU-based rendering pushes work to the display server and gives the illusion of being faster and more efficient than it really is.)

Once again, what is the exemplar of an efficient terminal then. We've already established ghostty doesn't operate the way you think it should so how can it turn out good?

j / k navigate · click thread line to collapse