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Date: Mon, 9 Jul 2012 01:24:14 +0530
From: Sayantan Datta <>
Subject: Re: Rotate and bitselect investigation

On Sun, Jul 8, 2012 at 2:48 PM, Solar Designer <> wrote:

> On Sun, Jul 08, 2012 at 02:41:08PM +0530, Sayantan Datta wrote:
> > So the results are little slow on 570 and also on 4890. So if you want we
> > can have two binary kernel specifiaclly tailored for these two and one
> > general kernel for all other devices. Or we may go the opposite way too
> i.e
> > using binary for 7970.
> No, let's not bother with multiple kernel versions just because of this.
> Rather, if you have time, you may try optimizing SHA1_digest() further
> (based on the known constants for some W[] elements), such that it
> relies on the optimizer less.  I suspect that it's this reliance on the
> optimizer that results in bitselect() hurting performance on some cards.
> This suggests that the overall speedup we're seeing on 7970 is less than
> full as well - in other words, that there's some slowdown (more limited
> propagation of the known constants in the optimizer) and a greater
> speedup from bitselect() itself at once.  The slowdown portion may be
> avoided by better written source code.
> > Do you want me to commit it and push to git repo?
> Yes, please.  Thanks.
> Alexander

I was able to squeeze in another bitselect optimization in the kernel
resulting in 2% performance jump.

std2048@...l:~/bin/run$ ./john -te -fo=mscash2-opencl -pla=1
OpenCL platform 1: AMD Accelerated Parallel Processing, 2 device(s).
Using device 0: Tahiti
Optimal Work Group Size:128
Kernel Execution Speed (Higher is better):1.581469
Benchmarking: M$ Cache Hash 2 (DCC2) PBKDF2-HMAC-SHA-1 [OpenCL]... DONE
Raw:    103819 c/s real, 103819 c/s virtual


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