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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
aafbe1cc | 5 | OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - instrument references to memory bus |
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6 | |
7 | =head1 SYNOPSIS | |
8 | ||
9 | #ifdef OPENSSL_CPUID_OBJ | |
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10 | size_t OPENSSL_instrument_bus(int *vector, size_t num); |
11 | size_t OPENSSL_instrument_bus2(int *vector, size_t num, size_t max); | |
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12 | #endif |
13 | ||
14 | =head1 DESCRIPTION | |
15 | ||
16 | It was empirically found that timings of references to primary memory | |
17 | are subject to irregular, apparently non-deterministic variations. The | |
18 | subroutines in question instrument these references for purposes of | |
f367ac2b | 19 | gathering randomness for random number generator. In order to make it |
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20 | bus-bound a 'flush cache line' instruction is used between probes. In |
21 | addition probes are added to B<vector> elements in atomic or | |
22 | interlocked manner, which should contribute additional noise on | |
23 | multi-processor systems. This also means that B<vector[num]> should be | |
24 | zeroed upon invocation (if you want to retrieve actual probe values). | |
25 | ||
c952780c | 26 | OPENSSL_instrument_bus() performs B<num> probes and records the number of |
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27 | oscillator cycles every probe took. |
28 | ||
c952780c | 29 | OPENSSL_instrument_bus2() on the other hand B<accumulates> consecutive |
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30 | probes with the same value, i.e. in a way it records duration of |
31 | periods when probe values appeared deterministic. The subroutine | |
32 | performs at most B<max> probes in attempt to fill the B<vector[num]>, | |
33 | with B<max> value of 0 meaning "as many as it takes." | |
34 | ||
1f13ad31 | 35 | =head1 RETURN VALUES |
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36 | |
37 | Return value of 0 indicates that CPU is not capable of performing the | |
38 | benchmark, either because oscillator counter or 'flush cache line' is | |
39 | not available on current platform. For reference, on x86 'flush cache | |
40 | line' was introduced with the SSE2 extensions. | |
41 | ||
42 | Otherwise number of recorded values is returned. | |
99ec4fdb | 43 | |
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44 | =head1 COPYRIGHT |
45 | ||
61f805c1 | 46 | Copyright 2011-2018 The OpenSSL Project Authors. All Rights Reserved. |
e2f92610 | 47 | |
4746f25a | 48 | Licensed under the Apache License 2.0 (the "License"). You may not use |
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49 | this file except in compliance with the License. You can obtain a copy |
50 | in the file LICENSE in the source distribution or at | |
51 | L<https://www.openssl.org/source/license.html>. | |
52 | ||
53 | =cut |