I'm experiencing performance issues in Krita 2.9.10 when it comes to using brushes.
Simple brushes work fine, but these brushes with smudge, custom texture or other advanced functions can delay.
Here's a testing file with log (let me know, if you need some more info):
http://www.speedyshare.com/WrJBP/log.7z

System specs:
Windows 7 64 bit
CPU Intel Core i5-2300 2.8 GHz
GPU AMD Radeon R9 280
8 GB RAM