OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - instrument references to
size_t OPENSSL_instrument_bus(int *vector, size_t num);
size_t OPENSSL_instrument_bus2(int *vector, size_t num, size_t max);
It was empirically found that timings of references to primary memory are
subject to irregular, apparently non-deterministic variations. The subroutines
in question instrument these references for purposes of gathering entropy for
random number generator. In order to make it bus-bound a 'flush cache line'
instruction is used between probes. In addition probes are added to
elements in atomic or interlocked manner, which should
contribute additional noise on multi-processor systems. This also means that
should be zeroed upon invocation (if you want to retrieve
actual probe values).
probes and records the
number of oscillator cycles every probe took.
on the other hand accumulates
consecutive probes with the same value, i.e. in a way it records duration of
periods when probe values appeared deterministic. The subroutine performs at
probes in attempt to fill the vector[num]
value of 0 meaning "as many as it takes."
Return value of 0 indicates that CPU is not capable of performing the benchmark,
either because oscillator counter or 'flush cache line' is not available on
current platform. For reference, on x86 'flush cache line' was introduced with
the SSE2 extensions.
Otherwise number of recorded values is returned.
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Licensed under the OpenSSL license (the "License"). You may not use
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