2004-08-31 21:02:17 +00:00
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<?php
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require_once("docutil.php");
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page_head("CPU scheduling in Version 4+");
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echo "
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<h3>Time-slicing</h3>
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<p>
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Starting with version 4.00,
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the BOINC core client does <b>time-slicing</b>.
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This means that the core client may switch back and forth
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between results of different projects.
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This is done in a way that allocates CPU time
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according to the 'resource shares' you have assigned to each project.
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<p>
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For example, suppose you participate in SETI@home
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with resource share 100
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and Predictor@home with resource share 200.
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A single-processor machine might be scheduled as follows:
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<pre>
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1:00 - 2:00: SETI@home
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2:00 - 3:00: Predictor@home
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3:00 - 4:00: Predictor@home
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4:00 - 5:00: SETI@home
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5:00 - 6:00: Predictor@home
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6:00 - 7:00: Predictor@home
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...
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</pre>
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A two-processor machine might be scheduled as follows:
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<pre>
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CPU 0 CPU 1
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1:00 - 2:00: Predictor@home SETI@home
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2:00 - 3:00: Predictor@home SETI@home
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3:00 - 4:00: Predictor@home Predictor@home
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4:00 - 5:00: Predictor@home SETI@home
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5:00 - 6:00: Predictor@home SETI@home
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6:00 - 7:00: Predictor@home Predictor@home
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</pre>
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In every 3 hour period,
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your computer spends 4 hours on Predictor@home
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and 2 hours on SETI@home, which is the desired ratio.
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<p>
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This feature is necessary to handle projects like
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<a href=http://climateprediction.net>Climate<i>prediction</i>.net</a>,
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whose work units take a long time (1 or 2 months)
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to complete on a typical computer.
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Without time-slicing, your computer would have to finish an
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entire work unit before it could start working on a different project.
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<h3>Preemption</h3>
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<p>
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When BOINC switches from one application to another,
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the first application is said to be <b>preempted</b>.
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BOINC can do preemption in two different ways;
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you can select this as part of your
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<a href=prefs.php>General Preferences</a>.
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<ul>
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<li>
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<b>Don't leave the suspended applications in memory</b> (default).
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Applications are preempted by killing them;
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they are later restarted, and resume from their last checkpoint.
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This saves virtual memory (swap space) but can waste CPU time,
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especially if applications checkpoint infrequently.
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<li>
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<b>Leave suspended applications in memory</b>.
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Applications are preempted by suspending them;
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they remain in virtual memory while preempted
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(they don't necessarily occupy physical memory).
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2005-06-02 21:38:20 +00:00
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</ul>
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2004-08-31 21:02:17 +00:00
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";
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page_tail();
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?>
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