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Date: Fri, 4 Sep 2020 10:02:55 +0200
From: Solar Designer <>
Subject: Re: rar-opencl performance

On Fri, Sep 04, 2020 at 01:50:02AM +0200, Axymeus wrote:
> Alright, looks like Windows 10 is not properly reporting GPU usage
> when running a PowerShell command... Looking at Afterburner I can see
> that both cRARk and JTR are actually using 100% GPU, but not
> constantly. There's a brief spike and a brief pause, but a much longer
> pause between each spike with JTR. CPU usage is about the same. Here
> is a visual comparison on the left of
> the graph usage cycle of cRARk and on the right usage cycle of JTR.

OK, so it's possibilities 1 or 2, but not 3.  (Of those I listed below.)

> Unfortunately I won't be able to provide the archive being used. And
> I'm not sure how to produce an equivalent, but I could give it a shot.

magnum, do you have any advice for Axymeus on what parameters of the
archive to look up and how, and how to replicate those?


> On Fri, Sep 4, 2020 at 1:31 AM Solar Designer <> wrote:
> >
> > On Fri, Sep 04, 2020 at 01:18:56AM +0200, Axymeus wrote:
> > > cRARk goes up to 20K p/s on this archive.
> >
> > This can mean one of several things:
> >
> > 1. cRARk handles the archive smarter, rejecting candidate passwords
> > earlier.  We do have early-reject in many cases, but apparently not
> > working as effectively in yours.  If this is the case, then it's
> > something magnum (a JtR developer) will want to improve in our
> > rar-opencl format, I guess.  You might want to provide to him a copy of
> > the archive - or preferably another "equivalent" archive with a known
> > password and no sensitive content.
> >
> > 2. cRARk handles the archive incorrectly, rejecting candidate passwords
> > early too aggressively, and might produce false negatives (miss the
> > correct password).
> >
> > 3. cRARk implements full archive processing on GPU now - probably not
> > the case.
> >
> > I guess #1 is most likely the case.
> >
> > What GPU utilization do you observe when cRARk is running on this
> > archive?  And CPU too?  This might give us a hint.
> >
> > Alexander

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