Manual Reference Pages - OPENSSL_INSTRUMENT_BUS2 (3)
OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - instrument references to memory bus
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 vector elements in atomic or
interlocked manner, which should contribute additional noise on
multi-processor systems. This also means that vector[num] should be
zeroed upon invocation (if you want to retrieve actual probe values).
OPENSSL_instrument_bus performs num probes and records the number of
oscillator cycles every probe took.
OPENSSL_instrument_bus2 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 most max probes in attempt to fill the vector[num],
with max 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.
|1.1.0-pre3 ||OPENSSL_INSTRUMENT_BUS (3) ||2016-02-15 |
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