private double usage0() {
        long[] currTicks = processor.getSystemCpuLoadTicks();
        double usage = processor.getSystemCpuLoadBetweenTicks(prevTicks);
        prevTicks = currTicks;
        return usage;
    }
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