1=pod 2 3=head1 NAME 4 5OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - instrument references to memory bus 6 7=head1 SYNOPSIS 8 9 #ifdef OPENSSL_CPUID_OBJ 10 size_t OPENSSL_instrument_bus(unsigned int *vector, size_t num); 11 size_t OPENSSL_instrument_bus2(unsigned int *vector, size_t num, size_t max); 12 #endif 13 14=head1 DESCRIPTION 15 16It was empirically found that timings of references to primary memory 17are subject to irregular, apparently non-deterministic variations. The 18subroutines in question instrument these references for purposes of 19gathering randomness for random number generator. In order to make it 20bus-bound a 'flush cache line' instruction is used between probes. In 21addition probes are added to B<vector> elements in atomic or 22interlocked manner, which should contribute additional noise on 23multi-processor systems. This also means that B<vector[num]> should be 24zeroed upon invocation (if you want to retrieve actual probe values). 25 26OPENSSL_instrument_bus() performs B<num> probes and records the number of 27oscillator cycles every probe took. 28 29OPENSSL_instrument_bus2() on the other hand B<accumulates> consecutive 30probes with the same value, i.e. in a way it records duration of 31periods when probe values appeared deterministic. The subroutine 32performs at most B<max> probes in attempt to fill the B<vector[num]>, 33with B<max> value of 0 meaning "as many as it takes." 34 35=head1 RETURN VALUES 36 37Return value of 0 indicates that CPU is not capable of performing the 38benchmark, either because oscillator counter or 'flush cache line' is 39not available on current platform. For reference, on x86 'flush cache 40line' was introduced with the SSE2 extensions. 41 42Otherwise number of recorded values is returned. 43 44=head1 COPYRIGHT 45 46Copyright 2011-2021 The OpenSSL Project Authors. All Rights Reserved. 47 48Licensed under the Apache License 2.0 (the "License"). You may not use 49this file except in compliance with the License. You can obtain a copy 50in the file LICENSE in the source distribution or at 51L<https://www.openssl.org/source/license.html>. 52 53=cut 54