OPENSSL_instrument_bus2(3ssl) - phpMan

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.



1.0.2k                                      2017-01-26                  OPENSSL_instrument_bus(3)

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