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Date: Wed, 02 Sep 2015 02:00:30 +0200
From: magnum <>
Subject: Re: 23% performance regression for brypt (Intel i5-4570

On 2015-04-12 12:14, Frank Dittrich wrote:
> Solar,
> you included the bcrypt related changes of bleeding-jumbo commit
> into core, but decided to not allow BF_X2 = 3 for AVX systems.
> (I guess this is because on well BF_X2 = 3 causes about 5% performance
> regression.)
> But for my system (64bit Linux, i5-4570 CPU), this causes a 23%
> performance regression.

Same here, on i7-3615QM (Ivy Bridge, AVX), OSX, gcc 4.9.2. Using X3 I 
get 27% boost for a non-OMP build, 22% for OMP and while it's just 4% 
boost for OMP+HT, it still is a boost.

> May be you also reconsider allowing BF_X2 = 3 for AVX.

If only well had a regression, perhaps decrease to X2 only for __AVX2__? 
Or maybe this is also about gcc version?

> Is there anything I can test, any more information you need to decide
> when BF_X2 should be 3 even for AVX, and when it shouldn't?


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