mirror of
https://github.com/openssl/openssl.git
synced 2024-12-09 05:51:54 +08:00
43 lines
1.6 KiB
Plaintext
43 lines
1.6 KiB
Plaintext
|
=pod
|
||
|
|
|
||
|
|
=head1 NAME
|
||
|
|
|
||
|
|
OPENSSL_instrument_bus[2] - instrument references to memory bus
|
||
|
|
|
||
|
|
=head1 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
|
||
|
|
|
||
|
|
=head1 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 B<vector> elements in atomic or
|
||
|
|
interlocked manner, which should contribute additional noise on
|
||
|
|
multi-processor systems. This also means that B<vector[num]> should be
|
||
|
|
zeroed upon invocation (if you want to retrieve actual probe values).
|
||
|
|
|
||
|
|
OPENSSL_instrument_bus performs B<num> probes and records the number of
|
||
|
|
oscillator cycles every probe took.
|
||
|
|
|
||
|
|
OPENSSL_instrument_bus2 on the other hand B<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 B<max> probes in attempt to fill the B<vector[num]>,
|
||
|
|
with B<max> value of 0 meaning "as many as it takes."
|
||
|
|
|
||
|
|
=head1 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.
|