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Date: Tue, 26 Jun 2012 01:54:45 +0200
From: magnum <john.magnum@...hmail.com>
To: john-dev@...ts.openwall.com
Subject: Re: OpenCL kernel max running time vs. "ASIC hang"
On 2012-06-26 01:27, Solar Designer 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?
Yes only now, and I was thinking more like 16K rounds x16. Not sure I
want to go there unless AMD says somewhere that this is actually a
design limit. Maybe they do? I would like to know the exact specified limit.
magnum
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