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Date: Sat, 8 Jul 2017 14:19:34 +0200
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: bcrypt-opencl on multiple GPUs?

Royce,

While our bcrypt-opencl is slower than it should be for NVIDIA Maxwell &
Pascal, per my testing it does work with multiple GPUs fine (with --fork).

I ran my test on one bcrypt cost 12 hash, like you did.

On Mon, Jul 03, 2017 at 05:58:29AM -0800, Royce Williams wrote:
> It's also notable that it takes more than 30 seconds between pressing
> a key and having status appear.

This is as expected for high bcrypt cost hashes being cracked on devices
that require a lot of candidate passwords to be buffered.

> Ah ... from looking at the nvidia-smi output, it's clear that there's
> only one child of john running, despite the --fork=6:

Yes, this is convincing evidence that only one john process uses a GPU.

Maybe there's some info in john.log - you could see from it where the
other child processes got stuck, or possibly even that they terminated
for some reason?  Also, do you see just one or multiple john processes
(including the forked children) in the process list?

When you rerun the command, please add "--verbosity=5".

Thanks,

Alexander

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