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Date: Tue, 26 Jun 2012 07:34:42 +0530
From: SAYANTAN DATTA <std2048@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: OpenCL kernel max running time vs. "ASIC hang"
On Tue, Jun 26, 2012 at 4:57 AM, Solar Designer <solar@...nwall.com> wrote:
> On Tue, Jun 26, 2012 at 01:06:08AM +0200, magnum wrote:
> > On 2012-06-26 00:27, Solar Designer wrote:
> > >I discussed this matter with Bit Weasil on IRC a few days ago.
> > >According to him, we shouldn't be trying to spend more than 200 ms per
> > >OpenCL kernel invocation, or we'll face random "ASIC hang" issues on AMD
> [...]
>
> > That's not an easy goal with slow formats. For RAR, with 256K rounds of
> > SHA-1, I currently don't get much below 2000ms on 7790, and that's with
> > GWS that produces a 40% slower c/s than what we currently use. For best
> > c/s we exceed 9 seconds. Then again, my code is made by a newbie. Making
> > it 10x faster would be nice for sure. But even Milen said his RAR kernel
> > ran for 2-3 seconds a while ago.
>
> I understand that reducing the amount of parallelism in a kernel
> invocation slows things down, but why not reduce the amount of work per
> kernel invocation by other means - specifically, in your example, why
> not reduce the number of SHA-1 iterations per kernel invocation? We may
> invoke the kernel more than once from one crypt_all() call,
> sequentially. For example, the 256k may be achieved by 256 invocations
> of a kernel doing 1k iterations. This would bring the 9 seconds down to
> 35 ms per kernel invocation. Perhaps the intermediate results can even
> stay in the GPU between those invocations.
>
> Have you considered that?
>
> Alexander
>
Wouldn't calling clEnqueNDRangeKernel too many times will cause a
performance hit? What about pausing the execution for some time as
requested by the user. Say we press 'P' which will pasue the execution so
that the user can perform the graphic oriented tasks and then resume the
execution when he is finished.
Regards,
Sayantan
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