mirror of https://github.com/BOINC/boinc.git
94 lines
2.9 KiB
HTML
94 lines
2.9 KiB
HTML
<title>Accounting and result validation</title>
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<body bgcolor=ffffff>
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<h2>Accounting and result validation</h2>
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<p>
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Participants are given <b>credit</b> for the computations performed
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by their hosts.
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These credits are used to generate web-site "leaderboards" showing
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individuals, teams, and categories (countries, CPU types, etc.)
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ranked by credit.
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It is expected that some users will attempt to get
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undeserved credit.
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<p>
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BOINC's unit of credit is CPU time times a weighted average
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of FP and integer speed and memory bandwidth.
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In principle it should reflect network transfer and disk storage as well.
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But it's hard to verify these activities,
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so for now they aren't included.
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<p>
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The core client reports the CPU time and the
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CPU metrics on which credit is based.
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These numbers can't be trusted in general.
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<p>
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Output files may be wrong.
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This can happen because of hardware
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failures, or because of tampering.
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<p>
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Both problems - credit-cheating and wrong results - can be addressed
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by <b>redundant computing</b> and <b>result validation</b>.
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In this approach, each workunit is processed at least twice.
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The project back end waits until a minimum number of results have been returned,
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then compares the results and decides which are considered correct.
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The notion of equality of results,
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and the policy for deciding which are correct,
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are project-specific.
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<p>
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The back end then marks correct results as "validated",
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finds the minimum reported credit for the correct results of a given workunit,
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and assigns this amount of credit to all the correct results.
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This ensures that as long as a reasonable majority of participants
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don't falsify credit, almost all credit accounting will be correct.
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<h3>The validation program</h3>
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BOINC supplies a utility program <b>validate</b>
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to perform validation and credit-granting.
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This program must be linked with two project-specific functions:
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<pre>
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int check_set(vector<RESULT> results, int& canonicalid, double& credit);
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int check_pair(RESULT& r1, RESULT& r2, bool& match);
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</pre>
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<b>check_set()</b> takes a set of results.
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If there is sufficient agreement,
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it selects one of them as the "canonical" result
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(returning its ID) and also decides what credit should
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be granted for correct results for this workunit.
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<p>
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<b>check_pair()</b> compares two results and returns match=true
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if they agree.
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<p>
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The file <b>validate_test.C</b> contains an example
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implementation of check_set() and check_pair().
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<hr>
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<h3>Implementation</h3>
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The following database fields are used:
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<p>
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<b>WORKUNIT</b>
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<dt> bool need_validate
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<dd>
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true iff this workunit has one or more results in state DONE
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and validate_state UNCHECKED
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<dt>
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int canonical_resultid
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<dd>
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nonzero if a conclusive check has been done for this WU;
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indicates the canonical result
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<p>
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<b>RESULT</b>
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<dt>
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int state
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<dd> INACTIVE, ..., DONE, ERROR
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<dt>
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int validate_state
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<dd>
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NEED_CHECK,
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VALID,
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INVALID
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