public synchronized double usage() {
        try {
            return usage0();
        } catch (Exception e) {
            return -1.0;
        }
    }
Returns the CPU usage between the last call of this method and now.
It returns -1.0 if an error occurs.

@return CPU load between 0 and 1 (100%)
tools/src/main/java/org/apache/kafka/tools/automq/perf/CpuMonitor.java