Date: Wed, 1 Feb 2012 02:06:00 +0000 From: Alex Sicamiotis <alekshs@...mail.com> To: <john-users@...ts.openwall.com> Subject: RE: DES with OpenMP > Maybe the code should assume that if there are 4 threads or less, that's > probably just one CPU chip - and use DES_bs_cpt=4 or 8 in that case. > This assumption will fail if the number of threads is deliberately > lowered to use only some cores in a multi-socket system, though. And it > will fail differently for bigger than quad-core CPU chips. Not great. > Hmm... yeah I can see the dilemma here of a parameter that can't be tweaked to suit all systems. > I suspect that it's nothing fundamental, but merely icc happening to do > register allocation or whatever better in one version of code vs. the > other. It might be the other way around in a slightly different build. > > These differences of a few percent are hard/unrealistic to turn in our > favor reliably without explicit assembly code and focus on a specific CPU. > > Alexander I managed to use icc in order to build various versions... I did a run with 1-4-8-16-32-64-128-256 values (values of 32+ slow down the cracking significantly so I'm not including 64+ and I only include 32 because it's the default value). I did two compilation series, one with -march=core2 and one without in order to examine how much is down to cpu-specific code. The core2 variant was about 16kb larger than the generic build and had similar if not slower performance. I tested with nice --10 and -test=20 on a shell / no desktop running - no apps running - most services shut down @ 4 GHz. What happened with gcc declining performance as the value went up, repeated itself with icc. I reached 9.36m c/s with des_bs_cpt values of 1 and 4... This is a gain of ~400k c/s with many salts. Interestingly, single salt gain was ~1.3m c/s (8.5m c/s rather than 7.2m c/s of the default 32 value). Running a single thread, I achieved 4750k c/s for many salts and 4473k c/s for one salt with values 1 to 4. Many salts gain over the 32 value was +100k, and single salt was +200k. This is less than what happened with the dual thread version which had larger gains. http://imageshack.us/f/408/resultsarein.png/
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