First, I'm not sure why s3qlctrl commands are documented twice, in the man page and on "Advanced S3QL Features". Second, the man page doesn't mention the "dropcache" command. Third, the advanced page states the following for "flushcache": "The command blocks until the cache has been flushed." That is the information I was looking for, so if true, it would help if also stated on the man page.
Issue #299 open