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Date: Wed, 21 Dec 2016 16:46:35 -0800
From: Andi Kleen <>
To: "Jason A. Donenfeld" <>
Cc: Netdev <>,,
	LKML <>,,
	David Laight <>, Ted Tso <>,
	Hannes Frederic Sowa <>,, Linus Torvalds <>,
	Eric Biggers <>,
	Tom Herbert <>,,,
	Jean-Philippe Aumasson <>
Subject: Re: [PATCH v7 6/6] siphash: implement HalfSipHash1-3 for hash tables

> 64-bit x86_64:
> [    0.509409] test_siphash:     SipHash2-4 cycles: 4049181
> [    0.510650] test_siphash:     SipHash1-3 cycles: 2512884
> [    0.512205] test_siphash: HalfSipHash1-3 cycles: 3429920
> [    0.512904] test_siphash:    JenkinsHash cycles:  978267

I'm not sure what these numbers mean. Surely a single siphash2-4
does not take 4+ million cycles? 

If you run them in a loop please divide by the iterations.

But generally running small code in a loop is often an unrealistic
benchmark strategy because it hides cache misses, primes
predictors, changes frequencies and changes memory costs,
but also can overload pipelines and oversubscribe

[see also page 46+ in]

So the numbers you get there are at least somewhat
dubious. It would be good to have at least some test which
is not just a tiny micro benchmark to compare before making


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