title: Setting spark running in local multiple threads mode, why only one cpu is running?
body: <p>I submit spark job to run in local machine with parameter --master local[6]. however, when I monitor the Spark UI, I found the spark.master is set to local instead of local[6]. I traced cpu status, it also shows only one cup is currently working, details as follows. </p>
  
  <pre><code>Tasks: 157 total,   1 running, 155 sleeping,   1 stopped,   0 zombie
  %Cpu0  :  0.3 us,  0.3 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu1  :  0.0 us,  0.3 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu2  : 99.7 us,  0.3 sy,  0.0 ni,  0.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu3  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu4  :  0.0 us,  0.3 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu5  :  0.3 us,  0.3 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu6  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  %Cpu7  :  0.0 us,  0.3 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
  KiB Mem:  49463808 total, 43074276 used,  6389532 free,   225860 buffers
  KiB Swap:  4194300 total,        0 used,  4194300 free.  8510192 cached Mem
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/aZQGH.png" alt="Spark UI spark.master info"></p>
  
  <p><img src="https://i.stack.imgur.com/Nub3M.png" alt="spark submit command"></p>