Date: Fri, 5 Jul 2013 13:36:27 +0200 From: magnum <john.magnum@...hmail.com> To: john-dev@...ts.openwall.com Subject: Re: bug: GPU use in CPU-only formats On 5 Jul, 2013, at 8:52 , Sayantan Datta <std2048@...il.com> wrote: > On Friday 05 July 2013 05:23 AM, magnum wrote: >> On 5 Jul, 2013, at 1:24 , magnum <john.magnum@...hmail.com> wrote: >>> I'm looking into some weirdness with mscash2-opencl when using multiple devices, I may have to tweak something. >> That problem was not introduced now so I'll leave it to Sayantan. It only happens with --test=0: >> >> $ ../run/john -t=0 -form:mscash2-opencl -dev=gpu >> Warning: doing quick benchmarking - the performance numbers will be inaccurate >> Device 0: GeForce GTX 570 >> Device 1: Tahiti (AMD Radeon HD 7900 Series) >> Optimal Work Group Size:256 >> Kernel Execution Speed (Higher is better):1.565550 >> Optimal Global Work Size:253952 >> WARNING: Device 0 is too slow and might cause degradation in performance. >> WARNING: Devices are NOT arranged in DECREASING order of performance and might cause degradation in performance. >> Benchmarking: mscash2-opencl, M$ Cache Hash 2 (DCC2) [PBKDF2-SHA1 OpenCL]... OpenCL error (CL_INVALID_WORK_GROUP_SIZE) in file (common_opencl_pbkdf2.c) at line (353) - (Enque Kernel Failed) > > What does the -t=0 option does ? It seems like 570 isn't being tested at all. For CPU formats, --test=0 (0 second test) [mostly] just self-tests - the benchmark figure is incorrect but all self-tests are completed. For OpenCL formats I emulate this by internally setting LWS=7 and GWS=49 whenever --test=0 is used. This way, the OpenCL formats test a whole lot quicker (and does not auto-tune, so we save even more time) with the same caveat that the benchmark figure will be low. For mscash2 I realize you try to balance LWS/GWS for heterogenous devices so the current behaviour is not really a bug. Either you could add some handling of this special case (should be easy), or just ignore it and document. Ideally, a "./john -t=0 -form:opencl" should test all OpenCL formats pretty quickly (but not properly benchmark them). magnum
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