Hello, Paolo. So, I'm currently verifying iocost in the FB fleet. Around three thousand machines running v5.2 (+ some backports) with btrfs on a handful of different models of consumer grade SSDs. I haven't seen complete loss of control as you're reporting. Given that you're reporting the same thing on io.latency, which is deployed on multiple orders of magnitude more machines at this point, it's likely that there's something common affecting your test setup. Can you please describe your test configuration and if you aren't already try testing on btrfs?
Thanks. -- tejun
