76 lines
5.1 KiB
HTML
76 lines
5.1 KiB
HTML
|
<?xml version="1.0" encoding="UTF-8"?>
|
||
|
|
<!DOCTYPE html
|
||
|
|
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
|
||
|
|
<html lang="en-us" xml:lang="en-us">
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
|
||
|
|
<meta name="security" content="public" />
|
||
|
|
<meta name="Robots" content="index,follow" />
|
||
|
|
<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
|
||
|
|
<meta name="DC.Type" content="concept" />
|
||
|
|
<meta name="DC.Title" content="Determine when to use simultaneous multithreading" />
|
||
|
|
<meta name="abstract" content="Simultaneous multithreading allows sharing of process facilities to run two applications or two threads of the same application at the same time. Find out more about this concept." />
|
||
|
|
<meta name="description" content="Simultaneous multithreading allows sharing of process facilities to run two applications or two threads of the same application at the same time. Find out more about this concept." />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="rzahxtune.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="../rzakz/rzakzqprcmlttsk.htm" />
|
||
|
|
<meta name="DC.Relation" scheme="URI" content="../books/sc410607.pdf" />
|
||
|
|
<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
|
||
|
|
<meta name="DC.Format" content="XHTML" />
|
||
|
|
<meta name="DC.Identifier" content="rzahxmultithread" />
|
||
|
|
<meta name="DC.Language" content="en-us" />
|
||
|
|
<!-- All rights reserved. Licensed Materials Property of IBM -->
|
||
|
|
<!-- US Government Users Restricted Rights -->
|
||
|
|
<!-- Use, duplication or disclosure restricted by -->
|
||
|
|
<!-- GSA ADP Schedule Contract with IBM Corp. -->
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
|
||
|
|
<link rel="stylesheet" type="text/css" href="./ic.css" />
|
||
|
|
<title>Determine when to use simultaneous multithreading</title>
|
||
|
|
</head>
|
||
|
|
<body id="rzahxmultithread"><a name="rzahxmultithread"><!-- --></a>
|
||
|
|
<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
|
||
|
|
<h1 class="topictitle1">Determine when to use simultaneous multithreading</h1>
|
||
|
|
<div><p>Simultaneous multithreading allows sharing of process facilities
|
||
|
|
to run two applications or two threads of the same application at the same
|
||
|
|
time. Find out more about this concept.</p>
|
||
|
|
<p>Although an operating system gives the impression that it is concurrently
|
||
|
|
executing a very large number of tasks, each processor in a symmetric multiprocessor
|
||
|
|
(SMP) traditionally executes a single task's instruction stream at any moment
|
||
|
|
in time. The QPRCMLTTSK system value controls whether to enable the individual
|
||
|
|
SMP processors to concurrently execute multiple instruction streams. Each
|
||
|
|
instruction stream belongs to separate tasks or threads. When enabled, each
|
||
|
|
individual processor is concurrently executing multiple tasks at the same
|
||
|
|
time. The effect of its use will likely increase the performance capacity
|
||
|
|
of a system or improve the responsiveness of a multithreaded application.
|
||
|
|
Running multiple instruction streams at the same time does not improve the
|
||
|
|
performance of any given task. As is the case with any performance recommendations,
|
||
|
|
results vary in different environments.</p>
|
||
|
|
<p>The way that multithreading is done depends on the hardware model, and
|
||
|
|
therefore, the performance capacity gains will vary. IBM<sup>®</sup> eServer™ 5<em>xx</em> models support this
|
||
|
|
approach through a concept called simultaneous multithreading (SMT). This
|
||
|
|
approach, called hyperthreading on some Intel<sup>®</sup> processors, shares processor facilities
|
||
|
|
to execute each task's instructions at the same time. Older processors use
|
||
|
|
an approach called hardware multithreading (HMT). In the hardware multithreading
|
||
|
|
approach, the hardware switches between the tasks on any long processing delay
|
||
|
|
event, for example, a cache miss. Some models do not support any form of multithreading,
|
||
|
|
which means the QPRCMLTTSK system value has no performance effect.</p>
|
||
|
|
<p>Because the QPRCMLTTSK system value enables the parallel use of shared
|
||
|
|
processor resources, the performance gains depend highly on the application
|
||
|
|
and the model. Refer to the <cite><span class="keyword">iSeries™</span> Performance
|
||
|
|
Capabilities Reference</cite> for guidelines about what performance gains
|
||
|
|
might be expected through its use. In some cases, some applications are better
|
||
|
|
served by disabling this system value.</p>
|
||
|
|
</div>
|
||
|
|
<div>
|
||
|
|
<div class="familylinks">
|
||
|
|
<div class="parentlink"><strong>Parent topic:</strong> <a href="rzahxtune.htm" title="When you have identified a performance problem, you will want to tune the system to fix it.">Tune performance</a></div>
|
||
|
|
</div>
|
||
|
|
<div class="relref"><strong>Related reference</strong><br />
|
||
|
|
<div><a href="../rzakz/rzakzqprcmlttsk.htm">QPRCMLTTSK system value</a></div>
|
||
|
|
</div>
|
||
|
|
<div class="relinfo"><strong>Related information</strong><br />
|
||
|
|
<div><a href="../books/sc410607.pdf" target="_blank">iSeries Performance Capabilities Reference PDF</a></div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
</html>
|