// Record the utilization change. (Since
			// len(ps) == len(out), we know len(out) > 0.)
			out[0] = addUtil(out[0], mu)
		} else {
			// Check for per-P utilization changes.
			for i := range ps {
				p := &ps[i]
				util := 1.0
				if stw > 0 || p.gc > 0 {
					util = 0.0
				}
				out[p.series] = addUtil(out[p.series], MutatorUtil{int64(ev.Time()), util})
			}
		}
	}

	// No events in the stream.