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author | marha <marha@users.sourceforge.net> | 2015-02-22 21:39:56 +0100 |
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committer | marha <marha@users.sourceforge.net> | 2015-02-22 21:39:56 +0100 |
commit | 462f18c7b25fe3e467f837647d07ab0a78aa8d2b (patch) | |
tree | fc8013c0a1bac05a1945846c1697e973f4c35013 /openssl/doc/crypto/OPENSSL_instrument_bus.pod | |
parent | 36f711ee12b6dd5184198abed3aa551efb585587 (diff) | |
download | vcxsrv-462f18c7b25fe3e467f837647d07ab0a78aa8d2b.tar.gz vcxsrv-462f18c7b25fe3e467f837647d07ab0a78aa8d2b.tar.bz2 vcxsrv-462f18c7b25fe3e467f837647d07ab0a78aa8d2b.zip |
Merged origin/release (checked in because wanted to merge new stuff)
Diffstat (limited to 'openssl/doc/crypto/OPENSSL_instrument_bus.pod')
-rwxr-xr-x | openssl/doc/crypto/OPENSSL_instrument_bus.pod | 42 |
1 files changed, 42 insertions, 0 deletions
diff --git a/openssl/doc/crypto/OPENSSL_instrument_bus.pod b/openssl/doc/crypto/OPENSSL_instrument_bus.pod new file mode 100755 index 000000000..4ed83e495 --- /dev/null +++ b/openssl/doc/crypto/OPENSSL_instrument_bus.pod @@ -0,0 +1,42 @@ +=pod + +=head1 NAME + +OPENSSL_instrument_bus, OPENSSL_instrument_bus2 - 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. |