LGWR and 'log file sync waits'

Kevin Closson has posted an insightful note on LGWR -- why sometimes the wait event 'log file sync' does not mean Redo Log File Write (ie I/O) waits. LGWR spends time in waiting on writes that it has posted but also in returning to post the sessions waiting on *it* to the effect that the writes have completed. It is the second part of the LGWR time that is the "processing" time which may not be getting enough CPU !