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Message-ID: <20130915000042.GC17101@openwall.com>
Date: Sun, 15 Sep 2013 04:00:42 +0400
From: Solar Designer <solar@...nwall.com>
To: john-users@...ts.openwall.com
Subject: Re: --fork using different OpenCL devices
magnum -
On Mon, Sep 09, 2013 at 01:08:00AM +0200, magnum wrote:
> On 8 aug 2013, at 05:30, Solar Designer <solar@...nwall.com> wrote:
> > On Wed, Aug 07, 2013 at 09:32:49PM +0200, magnum wrote:
> >> The idea is to have -fork pick a different device (starting from 0 or picking from a given list) for each child. Picture having two 7990 cards for a total of four devices. Using "-fork=4" with an OpenCL format would pick device 0 for the mother process, device 1 for first child and so on.
> >
> > This would provide poor man's multi-GPU support. Unfortunately, in the
> > current implementation of --fork there's some use of signals - such as
> > to get the status line printed by all children on a keypress - and this
> > appears incompatible with AMD's SDK.
>
> How? Does it crash and burn or do we just not get the status print from children?
It used to crash (on any signal sent between the processes) in the same
way that it crashed on Ctrl-C (that is, with the
"../../../thread/semaphore.cpp:87: sem_wait() failed" message). However,
when I inadvertently invoked a GPU format along with --fork more
recently (with Catalyst 13.6 beta on "well"), this crash somehow did not
happen. I did not test it any further, so I don't know if it ran
correctly in other aspects.
You might want to do some testing with different Catalyst versions.
> So maybe if we say "-fork=4 -dev=0" (or omit -dev) we should fork but use one device, and if we say "-fork=4 -dev=1,2,3,4" we should fork and use different devices. That should be intuitive enough. And "-fork=4 -dev=0,1" would fork into four processes but using only two devices, with two processes using each device.
Makes sense.
Alexander
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