Graphite - possible to get percent of requests under SLA?

I’m building a grafana dashboard for our test environment, and I’m building out the gatling graphs right now.

The single-most important thing I could report on is, what percent of our requests are completing within our target of 500ms, and what percent are under our SLA, and what percent are over the SLA.

Any idea whether or not it is possible to get such a graph out of graphite, given the data that is being put in? Are there functions that could be applied that would produce the desired result?