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Date: Tue, 26 May 2015 20:22:50 +0200
From: magnum <>
Subject: Re: interleaving in SHA256 & SHA512

On 2015-05-26 09:26, Lei Zhang wrote:
> On May 25, 2015, at 4:05 PM, magnum wrote:
>> BTW for interleaving factors, you should not just try multiples
>> like 2, 4, 8. You need to try all of 2, 3, 4, 5 - and more than 5
>> is probably never worthwhile (if it is, I guess it indicates we
>> should look into the code instead of just bumping para). So maybe
>> you need to retry all those benchmark yet again ;-)
> Ok, here's a re-test on MIC, with both a OpenMP-enabled and a OpenMP-disabled build:

> sha512crypt
> x1
> Raw:    6262 c/s real, 26.1 c/s virtual
> x2
> Raw:    6606 c/s real, 27.9 c/s virtual
> x3
> Raw:    6658 c/s real, 28.1 c/s virtual
> x4
> Raw:    7029 c/s real, 29.6 c/s virtual
> x5
> Raw:    6946 c/s real, 30.3 c/s virtual

Not a lot, but indeed a little RoI. I was starting to think all this 
work was for no good :-)

Like I said on GitHub, sha512crypt is a bit tricky because it sorts 
lengths in order to avoid diverging threads. So there's not only 
SIMD_PARA and OMP_SCALE but also SIMD_COEF_SCALE and all three will 
affect each other to some degree.
Maybe when all SHA2 interleaving is stable we can find some better 
format for benchmarking, eg. pbkdf2-hmac-sha512. I have a feeling 
finding a perfect SIMD_PARA might involve decreasing a previously tuned 


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