Hi fellow krita users! I ran into an issue with krita and I'm not sure what to do. I start painting and after a few brush strokes it starts to lag extremely(extreme as in I have to wait seconds for it to finish a line). I'm writing to see if anyone has encountered this issue and if anyone knows how to solve it.

When the brush starts lagging the CPU usage spikes way up, however memory usage remains low. I'm on a fresh install of fedora 23, fully updated on a laptop with 4 gigs of ram, integrated intel graphics and a secondary nvidia card which I use through bumblebee (If used on krita the lag gets worse). I use wacom one tablet and the 2.9.8 version of Krita. The issue doesn't seem to be present when using mouse. I tried to fiddle with settings increased step of brush(which helped but only when the brush turned into dots separated by half-centimeter long spaces), I tried to change filtering options, disable texture buffering, increasing internal memory pool and nothing.
However, increasing undo memory swap WAY up into 500MB range seems to help, it delays and reduces lag and when the lag comes, I can wait a minute for it to go away which is still pretty annoying and it seems a bit over the top to give 500mb of memory just for undos. I would guess krita tries way too hard to save undo history, however I only give it a 30 step stack for undos. I did not encounter this issue in xubuntu with the same laptop.

I hope I gave enough info about the issue, if anyone has any tips I'd be really grateful. Thanks for any advice in advance!

Ok so I disabled OpenGL completely and the problem seems to have disappeared. I did a bigger painting while a youtube video played in background and I was also installing some software to stress test with heavy ram usage and no lags whatsoever.

What graphics card and driver were you using?

That would be an integrated intel HD Graphics 3000 with the nouveau drivers. EDIT: version of driver is 1.0.12-0.3.fc23 according to my package manager

Now I also tried to run it through my Nvidia GT 520M with bumblebee but it just throws "Legacy integer arithmetics implementation" and doesn't start. I don't know if that gives you any usefull information...but the intel graphics work nicely at least.

Well, if the nouveau driver is active then the intel chip isn't used -- and that explains the lag. The open source nvidia drivers are quite notorious.

Ok. I disabled nouveau drivers, I checked it's not loaded into kernel and the issue persists if I use OpenGL. Whether I run it through nvidia card with bumblebee and proprietary drivers from rpmfusion repos or through my intel graphics with X.Org X11 Intel video driver. So I don't think it's nouveau making trouble, bbswitch works with nouveau anyways and should shut it off correctly. Hmmm this is quite a pickle lol. I might try building my own nvidia driver package.

So when I run krita with nvidia card it fails to do a bunch of OpenGL calls so I guess my card isn't supported. However when using intel card and I run it through terminal, it throws these messages all the time, seems like at the beginning of a brush stroke:
Unexpected tool event has come to continuePrimaryAction while being mode 0 !
Sometimes it writes this , but not always, usually at the end of brush stroke:
Unexpected tool event has come to endPrimaryAction while being mode 0 !
These messages come up only when using OpenGL.

I have the same problem in fedora 23, the nouveau driver don't work very well and for the moment, there is no privative driver from Nvidia for Fedora 23, as they say in this post https://forums.geforce.com/default/topic/892550/geforce-drivers/fedora-23-nvidia-driver-problem/post/4715490/#4715490

There is no such thing as xserver 1.18 yet: the latest release is 1.17.99.902, also known as 1.18 release candidate 2. NVIDIA does not support prerelease or release candidate X servers, and it's kind of surprising to me that Fedora would ship an official distribution release with beta software for something as fundamental as the X server.

Support for the X server ABI in the upcoming xserver 1.18 release should be available in the next release of the NVIDIA driver.

So, as you mentioned the problem it solves disabling OpenGL completely