Ah.  `--loglevel` is actually a Yogi core option, not something specific to `yogi perf`.  I'll remove it from this plugin's help docs.  I simply copied over everything in YUI Benchmark and removed things that weren't applicable to this plugin.

In general though, `--loglevel` is the name shared by [Yogi](https://github.com/yui/yogi/search?q=loglevel&ref=cmdform) and [Yeti](https://github.com/yui/yeti/search?q=loglevel&ref=cmdform), hence my decision to use that name in YUI Benchmark.