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    <p>Another way you might be able to improve the precision of your measurements is:</p> <ul> <li>Do your calculations in nano-seconds, so elapsed time (using <code>System.nanoTime()</code> and CPU time are natively in nanos. Blocked and Waiting times should be converted since they are in millis.</li> <li>Implement an approximation of how long it takes to simply capture elapsed, cpu, blocked and waiting times. (Call this OVERHEAD.) You might do this in a static block somewhere. Do a JVM warmup loop first, keeping in mind that the JIT kicks in after 15000 method calls [by default ? depends on your JVM....], so a warmup loop of at least that size would be good. </li> <li>The run the post-warmup loop, take the total elapsed divided by the loop count and you will have your OVERHEAD value. </li> <li>Subtract OVERHEAD from your calculated method elapsed times to get a better idea of the code execution time of the method, or....</li> <li>Add OVERHEAD to your addition of CPU, Blocked and Waited to get closer to the actual wall time.</li> <li>Optionally recalculate OVERHEAD from time to time.</li> </ul> <p>It's not perfect, and it is certainly not exacting, but it might give you slightly better numbers.</p> <p>Here's some test code I ran to calculate my average OVERHEAD (Java 7, Windows 7, 64 bit). I tried to make sure no methods were being ellided, but your mileage may vary.</p> <pre><code>public class Overhead { static final ThreadMXBean tmx = ManagementFactory.getThreadMXBean(); public static void main(String[] args) { tmx.setThreadContentionMonitoringEnabled(true); tmx.setThreadCpuTimeEnabled(true); int loops = 15000; long sum = -1; long start = System.nanoTime(); for(int i = 0; i &lt; loops; i++) { sum = measure(); } long elapsed = System.nanoTime()-start; log("Warmup completed in [" + elapsed + "] ns. "); log("Sum:" + sum); start = System.nanoTime(); loops = loops * 2; for(int i = 0; i &lt; loops; i++) { sum = measure(); } elapsed = System.nanoTime()-start; long avg = (elapsed/loops); log("Test completed in [" + elapsed + "] ns. OVERHEAD: [" + avg + "] ns."); log("Sum:" + sum); } protected static long measure() { long s1 = System.nanoTime(); long bt = tmx.getCurrentThreadCpuTime(); ThreadInfo ti = tmx.getThreadInfo(Thread.currentThread().getId()); long blocked = ti.getBlockedTime(); long waited = ti.getWaitedTime(); long s2 = System.nanoTime(); return ((s2 - s1) + blocked + waited + bt); } public static void log(Object msg) { System.out.println(msg); } } </code></pre> <p>My output was as follows:</p> <pre><code>Overhead test Warmup completed in [43176164] ns. Sum:109201929 Test completed in [38482368] ns. OVERHEAD: [1282] ns. Sum:156002228 </code></pre>
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    1. POJMX: CPU + Blocked + Wait time = Wall time?
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