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Date: Mon, 4 Jun 2012 21:48:12 +0530
To:, NeonFlash <>
Subject: Re: JtR OMP Questions

On Mon, Jun 4, 2012 at 7:32 PM, NeonFlash <>wrote:

> I have a few questions regarding, JtR's OMP Feature:
> Is there a way to control how many logical cores of the multi core CPU are
> used by john-omp.exe? By default, it uses all the available logical cores
> of the CPU but I would like to control this manually.
> I did not see any such option listed in the help.
> Does the OMP feature apply only to few hash types? For instance, I can see
> the multiple CPU Cores being used for few hash types like DES, Blowfish but
> not for others like dynamic_12 and so on. An example from the benchmark:
> C:\JTR\run>john-omp.exe --format=DES --test=3
> Benchmarking: Traditional DES [128/128 BS SSE2]... (8xOMP) DONE
> Many salts:     8770K c/s real, 1162K c/s virtual
> Only one salt:  7713K c/s real, 1105K c/s virtual
> C:\JTR\run>john-omp.exe --format=dynamic_12 --test=3
> Benchmarking: dynamic_12: md5(md5($s).md5($p))  (IPB)  [SSE2i 10x4x3]...
> Many salts:     2723K c/s real, 2717K c/s virtual
> Only one salt:  1966K c/s real, 1969K c/s virtual
> Is there a way to use multiple CPU Cores with a hash type such as
> dynamic_12?
> What is the difference between OMP and MPI?
> On linux platform, I noticed in the Makefile of JtR, that we can enable
> the OMPFLAGS to compile the JtR with OpenMP Compatibility and there is also
> an option to use MPI with OpenMP.
> However, I would like to understand the difference between the two?
> Thanks.

Set OMP_NUM_THREADS=1,2,3,4....

bash$ OMP_NUM_THREAD=3 ./john -te -fo=raw-md5
it will use only 3 threads.

While openMP is generally used for fine grain parallelism like within a
specific format. On the other hand MPI is generally used for task level
parallelism e.g two or more instances of john.


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