phc-discussions - Re: [PHC] Where do authors get these numbers?

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Date: Sun, 6 Sep 2015 07:28:44 +0100
From: Samuel Neves <sneves@....uc.pt>
To: discussions@...sword-hashing.net
Subject: Re: [PHC] Where do authors get these numbers?

On 09/06/2015 07:16 AM, Dmitry Khovratovich wrote:
> What CPU exactly are you testing on? That one has 2.1 GHz. We detected quite big difference in cycle/byte performance on similar CPU with different frequencies.

Cycles per byte are meant to be independent of the CPU frequency. When external memory gets involved, things do get a
little more complicated, though.

Is it possible that such differences are caused by Turbo Boost? Some processors overclock more than others; in
particular, a 2.1 GHz 4600U chip will overclock to 3.3 GHz, whereas a (say) 3.5 GHz 4770k chip will 'only' overclock to
3.9 GHz. Thus the former chip's timings will be significantly more distorted by Turbo Boost than the latter's, even
though they should both report roughly the same cycle-per-byte value in theory.