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Date: Sun, 5 Feb 2012 04:22:43 +0400
From: Solar Designer <>
Subject: Re: DES with OpenMP

On Sat, Feb 04, 2012 at 05:37:14PM +0000, Alex Sicamiotis wrote:
> Is this minor difference in DES (and larger negative impact in LM) down to a different resulting code due to the extra stuff, parameters etc, or are there any underlying changes like altered setting / coding differences between 1.7.9 and j5 regarding the cracking procedure itself?

Normally, I'd guess that it's due to different relative placement of
code from different source files in these builds, and/or the same for
data.  It is unfortunately sort of normal for fast hashes like LM to be
significantly affected by this.  However, I think that Core 2's L1
instruction and data caches are 8-way, so this effect should be pretty
minimal on your CPU.  It could be something else, then.  I am not aware
of specific relevant differences (neither code nor parameters) between
these versions.

> By the way in both 1.7.9 and jumbo, when I run with omp_num_threads=2, the program runs with a nice set to 0 by default. When threads=1, nice goes to 19. (Bug?)

Documented feature, although it'd be nice to come up with a better
solution where "Idle = Y" could work with OpenMP.  doc/CONFIG says:

Idle = Y|N

If set to "Y" (yes), John will try to use idle processor cycles only,
thereby greatly reducing its impact on other system processes.  The
impact on performance of John itself is negligible except on otherwise
overloaded systems.  This setting does not affect John's startup time
and non-cracking invocations of John; it only affects the actual
cracking.  The default is "Y" (yes).

Starting with version 1.7.7, this setting is ignored for OpenMP-enabled
hash types when the actual number of threads is greater than 1.
Unfortunately, it did not work right at least with GNU libgomp on Linux.


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