I was putting together a set of drawing stations for a convention last week (I can talk about that in a different thread if you like) and ended up attempting to install and run Krita on six different computers. Quite a few of them exhibited heavy brush lag out of the box. I eventually found a solution that allowed even the oldest machine to run Krita without lag, at least for the 1600x1200 canvas size I was testing. It turns out the brush lag and the black screen on many Intel integrated machines are related. Bad drivers. Unchecking Display -> OpenGL both solved the brush lag and black screen problems on all three of the computers that had them. "STATUS" is the out-of-box behavior. Here's details:

Machine 1
CPU: i5-4670K
GPU: Radeon R9 270X
RAM: 4GB
OS: Windows 7
Krita version: 2.9.9
STATUS: works

Machine 2
CPU: i7-5557u
GPU: Iris 6100 (integrated)
RAM: 8GB
OS: Windows 8.1
Krita version: 2.9.7
STATUS: works

Machine 3 (Linux Mint)
CPU: i3-5010u
GPU: HD 5500 (integrated)
RAM: 8GB
OS: Linux Mint 17.2
Krita version: 2.9.9
STATUS: Black Canvas

Machine 3 (Ubuntu)
CPU: i3-5010u
GPU: HD 5500 (integrated)
RAM: 8GB
OS: Ubuntu 15.10
Krita version: 2.9.9
STATUS: corrupted pixels on canvas

Machine 4
CPU: i5-2537M
GPU: HD 3000 (integrated)
RAM: 4GB
OS: Windows 7
Krita version: 2.9.9
STATUS: works

Machine 5 (Windows)
CPU: E-350
GPU: Radeon 6310 (integrated)
RAM: 2GB
OS: Windows 7 64bit
Krita version: 2.9.8
STATUS: Brush Lag

Machine 5 (Linux Mint)
CPU: E-350
GPU: Radeon 6310 (integrated)
RAM: 2GB
OS: Linux Mint 17.2 64bit
Krita version: 2.9.9
STATUS: Brush Lag

Machine 6
CPU: Dual Opteron 246
GPU: Radeon HD 2600 AGP
RAM: 2GB
OS: Linux Mint 17.2 64 bit
Krita version: 2.9.9
STATUS: Brush Lag

It was the 3rd machine that gave me the idea of unchecking the OpenGL box on the machines with brush lag. The canvas isn't quite a pretty, but every single computer on this list was able to take input from a Wacom tablet and put it on the screen without lag when the OpenGL box was unchecked. Even the *ancient* Dual Opteron. I think in both Linux and Windows, the renderer is silently failing back to software rendering if OpenGL 2.0 isn't available. Since there is a redraw request for every little pen motion, the CPU quickly gets behind. If that is the case, we may want Krita to check more carefully and run it's own software draw as needed. It seems to work much faster.

Of note, it turns out Intel support of Linux is *REALLY BAD*. They only commit to support the latest 6-month release of Ubuntu and Fedora. They actually disable older drivers of long-term OSs as they break instead of maintaining them. This means users of Ubuntu LTS, Linux Mint, Red Hat, and CentOS are currently out of luck.

I hope this helps, and that I have not posted something incorrect.

Thanks, this is really useful.

We discovered that AMD processors have trouble with VC, which we use to optimise, so Krita 2.9.10 and up will have an option to turn off Vector Optimisations.

It will also have a 'OpenGL' logging option, so it'll be interesting to look at that. (And I have experienced the software-emulation of OGL 2.1 myself. It was rather infuriating)

Oh good. The same type of multi-system setup is likely to happen again in six months. If I see anything useful, I will post it.