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Date: Tue, 9 Mar 2021 19:00:25 +0100
From: Solar Designer <>
Subject: Re: Multi-gpu setup

On Mon, Mar 08, 2021 at 04:22:47PM +0100, Micha?? Majchrowicz wrote:
> Quick question. Does john splits gpu tasks equally?

When you use "--fork" matching your GPU count, yes, it tries to split

> I just run a
> md5crypt dict attack on a multi gpu system and noticed one of gpus
> finished way faster than other one. If so can specify how big
> percentage will go to one gpu and how big to other ?

Not really, but as a hack you can list your faster GPU multiple times,
like this:

./john -fork=3 -dev=1,1,2 -format=something-opencl hash

This will run two concurrent instances of the OpenCL kernel on device 1,
but only one instance on device 2, still splitting the work between the
three instances equally - thus, giving device 1 twice more work.

As a cleaner workaround, you can run separate instances with "--node":

./john -se=1 -dev=1 -node=1-2/3 -format=something-opencl hash

and concurrently:

./john -se=2 -dev=2 -node=3/3 -format=something-opencl hash


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