Date: Wed, 21 Dec 2016 16:46:35 -0800 From: Andi Kleen <ak@...ux.intel.com> To: "Jason A. Donenfeld" <Jason@...c4.com> Cc: Netdev <netdev@...r.kernel.org>, kernel-hardening@...ts.openwall.com, LKML <linux-kernel@...r.kernel.org>, linux-crypto@...r.kernel.org, David Laight <David.Laight@...lab.com>, Ted Tso <tytso@....edu>, Hannes Frederic Sowa <hannes@...essinduktion.org>, edumazet@...gle.com, Linus Torvalds <torvalds@...ux-foundation.org>, Eric Biggers <ebiggers3@...il.com>, Tom Herbert <tom@...bertland.com>, davem@...emloft.net, luto@...capital.net, Jean-Philippe Aumasson <jeanphilippe.aumasson@...il.com> 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 resources. [see also page 46+ in http://halobates.de/applicative-mental-models.pdf] 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 conclusions. -Andi
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