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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"><head>	<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />	<style type="text/css">	body { font-family: Verdana, Arial, Helvetica, sans-serif;}	a.at-term {	font-style: italic; }	</style>	<title>Disadvantages of OpenMP</title>	<meta name="Generator" content="ATutor">	<meta name="Keywords" content=""></head><body> <p> Some disadvantages of OpenMP are:</p>

<ul>
  <li>OpenMP code can be run only on shared memory systems.</li>

    <ul>
    <li>Limits the number of processors that can ultimately be used.</li>
    </ul>
 

  <li>Data placement and locality may be serious issues.</li>

    <ul>
    <li>This is particularly important on ccNUMA architectures such as the SGI Origin, where it is desirable that needed data are local to the processor; the cost of remote memory accesses may be relatively high.</li>
    </ul>

  <li>Team [thread] creation overheads can be significant and may dominate unless enough work is performed in each parallel loop.</li>

     <ul>
     <li>You can use the <code>if</code> clause, for example, of the <code>parallel do/for</code> directive to dynamically decide whether to spawn a team of threads based on, e.g., the loop trip count.</li>
</ul>

<li>Implementing a coarse-grained solution in OpenMP is usually about as involved as constructing the analogous MPI application.</li>

</ul></body></html>

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