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Date: Wed, 17 Jul 2013 00:19:20 +0200
From: magnum <john.magnum@...hmail.com>
To: john-dev@...ts.openwall.com
Subject: Re: bug: GPU use in CPU-only formats

On 13 Jul, 2013, at 22:33 , Solar Designer <solar@...nwall.com> wrote:
> This problem is still present, and it manifests itself in an even worse
> way than I had thought.  Not only is there some use of the first GPU
> during CPU-only runs with an OpenCL-enabled build, but also CPU time is
> being wasted by some OpenCL-related overhead, which slows down CPU-based
> cracking (in some of my tests, by more than a factor of 2 - that's when
> OpenMP is also in use).  This is easily reproducible on our new dev box
> (which I'll create you accounts on shortly), where several ksoftirqd
> kernel threads appear high in "top" when running a CPU-only format in an
> OpenCL-enabled build of JtR.

So the GPUs start to run havoc just from a device query. In my world this is  clearly a driver bug. I will work around it once I get some time and inspiration occuring at the same time.

magnum

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