OCC is the sound you make when throttled

Back from distant climes to find an interesting tweet from Raptor relating to the POWER9 OCC. The OCC, or On-Chip Controller, monitors power usage and thermal stability, and can surface this information to the kernel via cpufreq. Raptor is asking users who get throttling warnings in dmesg to report them, though I haven't seen any such issues on my thermally constrained Blackbird or on this cool-running Talos II, and it's not clear how widespread the issue actually is.

Meanwhile, users who get weird OCC-related crashes when the POWER9 is in a stop state are encouraged to upgrade to the latest firmware release candidate to pick up this fix. This apparently is being triggered by recent kernel versions that enable deep power saving modes.