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Date: Wed, 18 Apr 2012 17:02:59 +0530
From: SAYANTAN DATTA <std2048@...il.com>
To: john-dev@...ts.openwall.com
Subject: System Responsiveness and GPU temps During Cracking on GPU

Hi Samuele,magnum and others

I was stress testing my gpu and MSCASH2 algorithm for some real scenarios.
So I loaded a 6 digit password("hd4890") hash in the file pw. This is what
I loaded.

sayantan:64d3e78d25d36de331cf680c6603f89b

Then I ran:

./john pw -fo=mscash2-opencl

After running for about 20 minutes i.e. nearly 350 crypt_all() calls on my
gpu it started producing errors. The clEnqueNDRangeKernel() started
failing. My GPU was running really hot(max 88C) and I think this is the
reason for the failure.   Also the desktop becomes unusable for 20 minutes
which is certainly very annoying.

Hence something must be done to resolve these issues.

Limiting the number of work groups helps in increasing system
responsiveness and reduce temps but the performance drops drastically.  Are
there any ways to limit the number of compute units. ie if I have 10 CUs
then only 9 CUs or less would be used for computation.

Regards,
Sayantan

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