john-users - Re: Unexpected speeds with o5logon and o5logon-opencl

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Message-ID: <20161124183523.GA8292@openwall.com>
Date: Thu, 24 Nov 2016 19:35:23 +0100
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: Unexpected speeds with o5logon and o5logon-opencl

Hi Kevin,

On Thu, Nov 24, 2016 at 12:43:31AM +0000, Kevin Miller wrote:
> I'm unsure if I'm the problem or have some broken installation but I would
> expect 3 GPU's to surpass the speed of 6-core CPU although it's quite the
> opposite in my case.
> 
> When running the o5logon-opencl format the GPU's do not seem utilize and
> appear idle while going through the process, the CPU is quicker!

Unfortunately, yes.  JtR's GPU support is still mostly limited to
so-called "slow hashes".  For some "fast hashes", we have on-GPU mask
mode, which makes them in fact run fast.  (And our mask mode can be
combined with other modes, to produce hybrid modes.)  Unfortunately, our
o5login-opencl lacks on-GPU mask mode currently, yet this is a fast
hash.  So you can't even remedy the problem by using mask mode, as you
would with some other fast hashes.  (You're currently trying to run
wordlist with rules, which would be inefficient with any fast hash.)

You may improve things a little bit by using each GPU more than once,
but it will still be very inefficient.

Your original command:

./john --devices=0,1,2 --rules=best64 --format=o5logon-opencl --wordlist=passwords.txt o5logon_hash.txt

(BTW, it used only 1 GPU since you didn't specify "--fork=3".)

Revised for two processes per GPU:

./john --devices=0,1,2 --fork=6 --rules=best64 --format=o5logon-opencl --wordlist=passwords.txt o5logon_hash.txt

or even for four processes per GPU:

./john --devices=0,1,2 --fork=12 --rules=best64 --format=o5logon-opencl --wordlist=passwords.txt o5logon_hash.txt

On CPU, you can also speed things up a little bit by using "--fork"
instead of OpenMP.  Your original command:

./john --rules=best64 --format=o5logon --wordlist=passwords.txt o5logon_hash.txt

Revised:

./john --fork=6 --rules=best64 --format=o5logon --wordlist=passwords.txt o5logon_hash.txt

Also, you may choose to run wordlist+rules on CPU, and non-wordlist
modes (incremental, mask, Markov) on GPU (actually, they run on CPU as
well, but they compute the hashes on GPU).  With wordlist+rules, the
bottleneck of candidate password generation is particularly bad.

> Below is some system info and examples to skim over.
> 
> http://pastebin.com/raw/1f2PEXEh

Thanks.  On future occasions, please post such info directly to the list
instead of via pastebin.

Alexander

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