After about a week of tests on freshly installed system i can conclude that two things affect on stutters 6.6 amd64 with all the patches included. To exclude hardware related problems I've changed AMD SOC PC to a new different one with the exactly the same configuration.
1. System works with minimum stutter if it had minimum filesystem transfers. Stutters appear every 10-30s and lasts <0.3s (no USB devices connected). 2. Stutters every 3-5s and lasts ~1s appear continuously when external USB3.0 storage is connected to xhci(4) and copy large amount of data ~150+Gb between local HDD and USB3 HDD. Both disks are softraid encrypted. While copying between disks main system HDD produce ahci0 errors and finally softraid0 errors. softraid0: sd1: i/o error 5 @ CRYPTO block 1757304592 ahci0: NCQ errored stol 1 is idle (00000004 active) softraid0: sd1: i/o error 5 @ CRYPTO block 129752048 softraid0: sd1: i/o error 5 @ CRYPTO block 1757319184 ahci0: NCQ errored slot 20 is idle (00200000 active) softraid0: sd1: i/o error 5 CRYPTO block 1745216016 3. When copying is stopped stutters every 3-5s are present as described above, and disappear after next reboot. If reboot isn't performed, system completely hangs in 1-2 days and next boot fsck find a LOT of DUP inodes. Most files affected are broken because of it. I changed HDD to the same *new* one to exclude HDD hardware potentional problems. There is no any problems such described above in 6.4amd64 at all. I think something has been changed between 6.4 - 6.6. Martin
