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Date: Fri, 29 Sep 2017 09:10:34 +0200
From: magnum <>
Subject: Re: OMP vs. OpenCL performance

On 2017-09-29 05:29, Scott I. Remick wrote:
> 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.

I presume your hashes are in the order of 500,000 iterations. If not, 
that's too slow.

> 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...

It's plausible. My (REALLY weak) GPU, a GT650M, outperforms my i7-3615QM 
2.30GHz by 20% (also 8 HT) or so. Heck, even my ridiculous "Intel HD 
Graphics 4000" can do half the speed of my CPU!

> 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.

Ensure you buy an nvidia with Maxwell (9xx) or Pascal (10xx) chipset. As 
you've seen, even a low budget one will be way faster than your CPU.


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