title: Trying to understand nvprof metrics, sm_efficiency and warp_execution_efficiency zero
body: <p>I am trying to understand the nvprof metrics. I am new to CUDA and therefore trying to understand which metrics is important for performance.</p>
  
  <p>I wrote a kernel for calculating the sum of absolute difference between matrices.</p>
  
  <p>Running on a Tegra X1, it averages at about 47ms, with 1584 blocks and 1024 threads per block.</p>
  
  <p>Running nvprof i get these metrics:</p>
  
  <pre><code>achieved_occupancy         Achieved Occupancy         0.982284    0.982284    0.982284
  warp_execution_efficiency  Warp Execution Efficiency  0.00%       0.00%       0.00%
  sm_efficiency              Multiprocessor Activity    0.11%       0.11%       0.11%
  branch_efficiency          Branch Efficiency          100.00%     100.00%     100.00%
  ipc                        Executed IPC               3.600738    3.600738    3.600738
  </code></pre>
  
  <p>How come the <code>Warp Execution Efficiency</code> and <code>Multiprocessor Activity</code> are so low, when the other metrics are so good? These are the right metrics to look at when profiling the general performance of a kernel, right?</p>