mirror of https://github.com/BOINC/boinc.git
109 lines
3.3 KiB
PHP
109 lines
3.3 KiB
PHP
<?php
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require_once("docutil.php");
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page_head("Computation credit");
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echo "
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<p>
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Each project gives you <b>credit</b> for the computations your
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computers perform for it.
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BOINC's unit of credit, the <b>Cobblestone</b> <sup>1</sup>,
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is 1/100 day of CPU time on a reference computer that does
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<ul>
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<li> 1,000 double-precision MIPS based on the Whetstone benchmark.
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<li> 1,000 VAX MIPS based on the Dhrystone benchmark.
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</ul>
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Eventually, credit may reflect network transfer and disk storage as well
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as computation.
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<h2>How credit is determined</h2>
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When your computer completes a result,
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BOINC determines an amount of <b>claimed credit</b>
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in one of two ways:
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<ul>
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<li>
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In general, the claimed credit is the result's CPU time multiplied
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by the CPU benchmarks as measured by the BOINC software.
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<b>NOTE:</b> the BOINC software is not optimized for specific processors.
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Its benchmark numbers may be lower than
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those produced by other programs.
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<li>
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Some applications determine claimed credit themselves,
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and report it to BOINC.
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This would be the case, for example, with
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applications that use graphics coprocessors or other non-CPU hardware.
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</ul>
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<p>
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Claimed credit is reported to a project
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when your computer communicates with its server.
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The <b>granted credit</b> that you receive may
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be different from the claimed credit,
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and there may be a delay of a few hours or days
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before it is granted.
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This is because some BOINC projects grant credit only after
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results have been <a href=intro_user.php#credit>validated</a>.
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<h2>Recent Average Credit</h2>
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<p>
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Projects maintains two counts of granted credit:
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<ul>
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<li> <b>Total credit</b>:
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The total number of Cobblestones performed and granted.
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<li> <b>Recent average credit</b>:
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The average number of Cobblestones per day granted recently.
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This average decreases by a factor of two every week,
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according to the algorithm given below.
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</ul>
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<p>
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Both quantities (total and recent average)
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are maintained for each user, host and team.
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<p>
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Each time new credit granted,
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the following function is used to update the
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recent average credit of the host, user and team:
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<pre>",htmlspecialchars("
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// Update an estimate of \"units per day\" of something (credit or CPU time).
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// The estimate is exponentially averaged with a given half-life
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// (i.e. if no new work is done, the average will decline by 50% in this time).
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// This function can be called either with new work,
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// or with zero work to decay an existing average.
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//
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void update_average(
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double work_start_time, // when new work was started
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// (or zero if no new work)
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double work, // amount of new work
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double half_life,
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double& avg, // average work per day (in and out)
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double& avg_time // when average was last computed
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) {
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double now = dtime();
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if (avg_time) {
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double diff = now - avg_time;
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double diff_days = diff/SECONDS_PER_DAY;
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double weight = exp(-diff*M_LN2/half_life);
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avg *= weight;
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avg += (1-weight)*(work/diff_days);
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} else {
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double dd = (now - work_start_time)/SECONDS_PER_DAY;
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avg = work/dd;
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}
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avg_time = now;
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}
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#define CREDIT_HALF_LIFE (SECONDS_IN_DAY*7)
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"),"
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</pre>
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<hr noshade size=1>
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<sup>1</sup> Named after Jeff Cobb of SETI@home
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";
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page_tail();
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?>
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