OPENSSL_instrument_bus(3) OpenSSL OPENSSL_instrument_bus(3)NAME
OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - instrument references
to memory bus
SYNOPSIS
#ifdef OPENSSL_CPUID_OBJ
size_t OPENSSL_instrument_bus (int *vector,size_t num);
size_t OPENSSL_instrument_bus2(int *vector,size_t num,size_t max);
#endif
DESCRIPTION
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
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.
1.0.2f 2016-01-28 OPENSSL_instrument_bus(3)
