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Date: Sat, 3 Mar 2018 15:39:58 +0100
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Getting full performance out of multiple GPU's

On Sat, Mar 03, 2018 at 03:15:58PM +0100, Piotr Dobrogost wrote:
> On Sat, Mar 3, 2018 at 1:11 PM, Solar Designer <solar@...nwall.com> wrote:
> > GPU memory utilization may
> > vary depending on actual needs - there's no universally correct/expected
> > level of GPU memory utilization.
> 
> True but still you expected near 100% and I think it's reasonable
> expectation.

No, I didn't expect that and it's not a reasonable expectation.  magnum
has just illustrated that with an example.

Let's troubleshoot the low GPU time utilization:

> Command is
> $ john --format=gpg-opencl --fork=8 --dev=2,3,4,5,6,7,8,9 test.txt.gpg

Oh, OK.  So, as seen per the log file you sent you have a young session
that is still frequently switching between incremental mode's lengths,
trying to test candidate passwords in a more optimal order.  To achieve
a steady speed in terms of candidate passwords tested per second, and
full GPU utilization, you'll need to either let this session run for
much longer or instead run attacks that are a better fit for in those
terms right away - such as locking incremental mode to a specific length
(with "--min-length" and "--max-length") or running a large wordlist.
Please try that and let us know of the results.

> where test.txt.gpg is result of
> $ gpg --symmetric --passphrase 'ala ma kota' test.txt

This passphrase is unlikely to be cracked against that file type soon,
unless you focus the attack.

> john.log:

Actually, I meant output seen on the terminal - not the log file - but
this works, too.  It's missing the reported speeds, though.

Alexander

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