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Date: Fri, 19 Jul 2013 11:30:30 +0200
From: magnum <john.magnum@...hmail.com>
To: john-dev@...ts.openwall.com
Subject: Re: bug: GPU use in CPU-only formats

On 17 Jul, 2013, at 0:19 , magnum <john.magnum@...hmail.com> wrote:
> 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.

Hopefully this is fixed for good now. No OpenCL initialization whatsoever happens untill an OpenCL format calls opencl_init(). Thanks to Claudio for fixing the missing pieces.

magnum

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