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Date: Sun, 21 Jun 2015 00:04:30 +0300
From: Solar Designer <solar@...nwall.com>
To: john-dev@...ts.openwall.com
Subject: Re: bcrypt-opencl local vs. private memory

magnum, Sayantan -

On Tue, Jun 16, 2015 at 05:06:40PM +0300, Solar Designer wrote:
> Sayantan took care of this at the time, in commit
> 97545b7ab51a4e8ddccba1a098f5448d808ae39b which includes:
> 
> #if gpu_nvidia(DEVICE_INFO)
> #define MAYBE_LOCAL             __private
> #else
> #define MAYBE_LOCAL             __local
> #endif
> 
> I've just tested this on our GTX 570 as well, and unfortunately it
> actually hurts performance there.  (Even though it was helping on our
> TITAN a bit.)  With the above commit, I am getting around 400 c/s.
> With forced use of __local, it's around 1200 c/s.
> 
> I merely want to document this in here.  I am not suggesting making any
> further change yet.  Either of these speeds is quite low anyway.
> 
> I am currently discussing bcrypt on GPU with Alain (via off-list
> e-mail), who managed to achieve much higher speeds anyway, including on
> his GTX 590 (per GPU).

(Un)fortunately, Alain's initial results that I mentioned above were
wrong.  So no "much higher speeds" for us.  I think we need to fix the
original issue described above somehow.  magnum, can we possibly have
this local vs. private bit autodetected along with GWS and LWS?

Alexander

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