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Date: Thu, 11 Mar 2021 13:20:47 +0100
From: Solar Designer <>
Subject: Re: Multi-gpu setup

On Wed, Mar 10, 2021 at 08:25:07PM +0100, Micha?? Majchrowicz wrote:
> > 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
> This looks interesting. I already switched to separate dictionaries
> for every gpu on each node for now.

You should be able to replace that with usage of "--node".

> Tough with your syntax I noticed
> you do NOT use --fork so does that mean with -se

As magnum explained "-se" is simply short for "--session", and is used
to specify different session names so that you can run both in the same
directory and writing to the same pot file.

> it will not require -node=1-15/28 to run 15 forks for single gpu ? :)

Right, this will not run any forked processes.  There will be just one
process per GPU.  The range of node numbers merely allocates a portion
of work to that process.

If your two GPUs differ in speed e.g. by a factor of 13, you can do:

./john -se=1 -dev=1 -node=1-13/14 -format=something-opencl hash

and in another terminal or such:

./john -se=2 -dev=2 -node=14/14 -format=something-opencl hash

If this is part of a larger cluster (e.g., one of two such machines),
you can do e.g.:

./john -se=1 -dev=1 -node=1-13/28 -format=something-opencl hash
./john -se=2 -dev=2 -node=14/28 -format=something-opencl hash

on one machine, and:

./john -se=3 -dev=1 -node=15-27/28 -format=something-opencl hash
./john -se=4 -dev=2 -node=28/28 -format=something-opencl hash

on the other.

I used non-overlapping session names here just in case you have a
network filesystem, but if you use separate directories you can as well
reuse session names between machines - or you can use non-overlapping
names anyway to avoid getting confused.


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