title: is system(const char *command) lead to cpu sys 100%
body: <p>I create one background thread B,and in func of B, </p>
  
  <pre><code>void func()
  {
    system('gzip -f text-file'); // size of text-file is 100M
    xxx
  }
  </code></pre>
  
  <p>I found sometime the sys of one cpu(my server has more than one cpu core） is 100%.
  strace the progress, I found clone syscall consume more than 3 seconds, which is almost execution time of gzip.</p>
  
  <pre><code>**17:46:04.545159** clone(child_stack=0, flags=CLONE_PARENT_SETTID|SIGCHLD, parent_tidptr=0x418dba38) = 39169
  **17:46:07.432385** wait4(39169, [{WIFEXITED(s) &amp;&amp; WEXITSTATUS(s) == 0}], 0, NULL) = 39169
  </code></pre>
  
  <p>so my question is,
  1. is system('gzip -f text-file'） lead to 100% cpu sys ?
  2. what is the root cause</p>