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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 randomness 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 VALUES
       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.

COPYRIGHT
       Copyright 2011-2018 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (the "License").  You	may not	use
       this file except	in compliance with the License.	 You can obtain	a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

1.1.1d				  2019-09-10	     OPENSSL_INSTRUMENT_BUS(3)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | COPYRIGHT

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