title: CPU Usage while packet forwarding
body: <p>I'm trying to measure the CPU usage on a dual core ARM Cortex A9 processor to benchmark a it. It will be used a router. I enabled ip forwarding and I'm running iperf tests along with monitoring the CPU usage using top. I'm a little confused about interpreting the results from <strong><em>top</em></strong>.</p>
  
  <pre><code>Cpu0  :  0.0%us,  0.5%sy,  0.0%ni, 59.1%id,  0.0%wa,  0.0%hi, 40.5%si,  0.0%st
  Cpu1  :  0.0%us,  0.0%sy,  0.0%ni,100.0%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
  </code></pre>
  
  <p>1) During packet forwarding why is the kernel usage at 0.5% compared to softirq percentage 40.5%? So the effective CPU usage is (40.5 + 0.5)%?</p>
  
  <p>2) Why is the 2nd CPU completely idle?</p>
  
  <p>Thanks!</p>