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Date: Tue, 13 Nov 2012 10:28:15 -0200
From: Claudio André <claudioandre.br@...il.com>
To: john-dev@...ts.openwall.com
Subject: Re: Clear keys
Em 12-11-2012 16:50, magnum escreveu:
> On 12 Nov, 2012, at 13:33 , Claudio André <claudioandre.br@...il.com
> <mailto:claudioandre.br@...il.com>> wrote:
>> Hi, i tried to use clear_keys (as in commitba10ced)
>>
>> But it hurts performance. Did i understand anything wrong?
>
> Probably not. I was going to bring this up too. Many parameters are
> involved.
>
> I did this for ntlmv2-opencl as it's running at speeds where this has
> significance (currently ~ 18M c/s at best). My original code did a
> 64-byte blind memset per key, first thing in set_key(). I changed it
> to memsetting the whole array at once in clear_keys() and it got a
> little faster on all hardware I have tested. But not a lot faster. I
> guess the original method makes better use of the cache (after that
> memset, cache is warm for the succeding uincode translation) while the
> huge memset is more effective in terms of SSE/AVX/etc optimized code.
>
> Anyway, that is a whopping 128 MB memset when running on the 7970 and
> normally less than 1/3 of each key will actually be dirty. So I
> thought there ought to be a better way. Just for the hell of it I
> tried making a trivial clear_keys kernel but no matter how fast that
> is, the transfer time makes it useless (unless I start juggling with
> two buffers).
>
> Then I moved the clearing back to set_key() - but in a way that does a
> 32-bit word at a time and that stops when it reaches already clear
> memory. This is faster on most gear I've tried (including Bull w/
> GTX570) but has a huge impact on the Tahiti (a.k.a 7970) that
> I really can't explain (speed drops to like 25% of original blind
> memset) despite it will normally not have to clean more than one word
> - if that. So for now I settled for the clear_keys() memset. I guess I
> could adopt to hardware and chose between these methods at runtime.
>
> It could be that the self test vectors happen to produce worse
> results (very long keys mixed with shorter) with that last experiment
> than what would be the normal case in real life. I might do more
> experiments later.
>
> magnum
I will Keep watching.
Thanks.
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