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Date: Thu, 30 Apr 2020 11:34:42 +0200
From: Solar Designer <>
Subject: Re: Reduce CPU load. Is it possible?

On Wed, Apr 29, 2020 at 11:03:15PM +0000, oayz wrote:
> I have 4 cores. Running all 4 as    start /affinity 0xffffffff \JOHN\run\john.exe
>  (left side of plots) than with only cores 3 and 4 as    start /affinity 0xfffffffe \JOHN\run\john.exe
> (right side)

The message had a screenshot attached.  We don't use screenshots here,
and the list is configured to automatically strip images.  Luckily, your
description is good enough on its own, which is how it should be.

> But in both cases JtR says "will use 4 OpenMP threads"

That's what I suspected.  So don't use this approach, it is inefficient.
Use OpenMP's own settings instead, like I had suggested.

This discussion got me thinking: maybe we should add a john.conf setting
to limit the number of threads.  It'll be the same as or similar to
OMP_NUM_THREADS, but we'll be able to give people instructions that are
independent of OS and shell.


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