Date: Sun, 4 Sep 2016 21:35:16 +0200 From: Sebastian Heyn <sebastian.heyn@...oo.de> To: john-users@...ts.openwall.com Subject: Re: Question regarding CPU load on GPU tasks Thank you for clarification. I think that means for now: a new psu and graphcics card. Excellent! Am 02.09.2016 um 19:20 schrieb magnum: > On 2016-09-02 13:53, Sebastian Heyn wrote: >> Now I noticed when I run a wpapsk-opencl vs a wordlist, the cpu load >> on a single core is 100% solid. > > I presume we're not talking about running OpenCL on CPU here. Are you > using an nvidia GPU? A silly property of their OpenCL runtime is it > busy-waits for GPU events. So it looks like it's pegging the CPU but > in reality it does no work on it. > >> When I fork the task to 4, it is 4x100% (its a quad core cpu) - >> however the amount of passwords per second is the same. I dont know >> how to interpret that result. Is the cpu 100% flat out due to some >> loop in the code, or is it really 100% busy? If so the forking should >> show some improvement, right? > > For WPAPSK there's no point in forking a run with OpenCL formats > (unless you have several GPU's - then you'll fork one process per > GPU). If you really have 4 GPU's, it's the same answer as before: > Busy-waits. No real bottleneck. > >> I am asking because I wonder what would happen if I bought a larger >> gpu (or 2) - would the cpu become a bottleneck? > > Not for this format anyway. It runs almost entirely on GPU(s). > >> Second question: Is openmpi also able to run gpu tasks on several >> machines? > > Sure. > > magnum > >
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