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Date: Thu, 28 Sep 2017 23:29:10 -0400
From: "Scott I. Remick" <>
Subject: OMP vs. OpenCL performance

Hello! I am taking my first stab playing around with JtR and it's 
certainly been enlightening. I have it working (I think) so I don't have 
any problems, but instead a question:

My system has an Intel Xeon E3-1276v3 (quad-core 3.6GHz) and an nVidia 
GeForce GTX 750. When I ran a pre-built binary (John the Ripper 
1.8.0-jumbo-1-5901-gbda8f8e+ OMP [linux-gnu 64-bit AVX2-ac]) and 
launched it, I saw it spawn 8 processes (hyperthreading) and was getting 
a measly 13-14 p/s on PBKDF2-HMAC-SHA512. But then I compiled a newer 
build w/ OpenCL (John the Ripper 1.8.0-jumbo-1-5908-g004c382 OMP 
[linux-gnu 64-bit AVX2-ac]), confirmed OpenCL and then forced it with a 
suitable --format option. That instance (even running simultaneously as 
the OMP instance) is getting currently 760 p/s (and rising, it was 590 
when I started) running on just the single GPU. This seems ridiculously 
faster...? Is the speed boost really that extreme? I don't even have a 
particularly powerful GPU... I figured the 4x CPU 3.6GHz cores 
cumulatively would beat it. Or did I mess up something with my CPU/OMP 

(This is all on Ubuntu 16.04, if it matters)

This is making me re-think my passively-cooled GPU card! :D For general 
usage it's fine (depending on the very-good case cooling), but if I'm 
going to start using this as a compute card I might want some sort of 
on-card cooling that can respond to GPU temps. 79'C currently, but it's 
been rising from the 54'C it was when I started 30 mins ago.

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