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Date: Fri, 4 Sep 2020 01:50:02 +0200
From: Axymeus <>
Subject: Re: rar-opencl performance

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.

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.

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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