Thomas Rushton ran into an oddity with sys.dm_os_ring_buffers:
Wait! Process Utilization + Idle adds up to waaaaay over 100…What’s going on?
My first thought was that the CPU was being throttled, so I checked the windows power options – for some really irritating reason, Windows defaults to a “balanced” power setting, which is rubbish for SQL Server.
That looks OK, but… if you check the CPU page of the Task Manager, things are a bit more interesting:
Unfortunately, the story doesn’t have a conclusion, but Thomas’s conjecture does make sense.