After updating my sister's laptop (which is on the stable update channel), with the latest update sync, and rebooting (after all, there are updates, especially kernel updates, that require rebooting), the OS has been rendered almost unusable, due to the GUI being utterly slow (~3 seconds before it would register that I had pressed the delete button when deleting a file, and Firefox complaining on every page that the page is slowing down the browser).
dmesg showed nothing of interest, and the only GUI-related thing that was unaffected was the cursor (anything nonGUI was also unaffected).
Installing the 5.6.19 .eopkg restored GUI performance.
I had a similar issue last week on my desktop (unstable update channel) with 5.10, however before I had the chance to notify about it, 5.10.1 was rolled out, and fixed all performance issue, so I had thought that it was a temporary regression that was already fixed.
My desktop utilizes an i5-4570 and a Radeon HD 6950 (still running, I had managed to partially conquer the temperature issues). with both iGPU and dGPU enabled (planning on passing through the iGPU to VMs when I have the chance.
My sister's laptop features a BayTrail Celeron (I forget the exact model), obviously with no dGPU).