mirror of https://github.com/openssl/openssl.git
54 lines
2.0 KiB
Plaintext
54 lines
2.0 KiB
Plaintext
=pod
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=head1 NAME
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OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - instrument references to memory bus
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=head1 SYNOPSIS
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#ifdef OPENSSL_CPUID_OBJ
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size_t OPENSSL_instrument_bus(int *vector, size_t num);
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size_t OPENSSL_instrument_bus2(int *vector, size_t num, size_t max);
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#endif
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=head1 DESCRIPTION
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It was empirically found that timings of references to primary memory
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are subject to irregular, apparently non-deterministic variations. The
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subroutines in question instrument these references for purposes of
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gathering randomness for random number generator. In order to make it
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bus-bound a 'flush cache line' instruction is used between probes. In
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addition probes are added to B<vector> elements in atomic or
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interlocked manner, which should contribute additional noise on
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multi-processor systems. This also means that B<vector[num]> should be
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zeroed upon invocation (if you want to retrieve actual probe values).
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OPENSSL_instrument_bus() performs B<num> probes and records the number of
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oscillator cycles every probe took.
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OPENSSL_instrument_bus2() on the other hand B<accumulates> consecutive
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probes with the same value, i.e. in a way it records duration of
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periods when probe values appeared deterministic. The subroutine
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performs at most B<max> probes in attempt to fill the B<vector[num]>,
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with B<max> value of 0 meaning "as many as it takes."
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=head1 RETURN VALUES
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Return value of 0 indicates that CPU is not capable of performing the
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benchmark, either because oscillator counter or 'flush cache line' is
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not available on current platform. For reference, on x86 'flush cache
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line' was introduced with the SSE2 extensions.
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Otherwise number of recorded values is returned.
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=head1 COPYRIGHT
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Copyright 2011-2018 The OpenSSL Project Authors. All Rights Reserved.
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Licensed under the Apache License 2.0 (the "License"). You may not use
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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L<https://www.openssl.org/source/license.html>.
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=cut
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