From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756724AbcANRxa (ORCPT ); Thu, 14 Jan 2016 12:53:30 -0500 Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:57988 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756090AbcANRx2 (ORCPT ); Thu, 14 Jan 2016 12:53:28 -0500 Date: Thu, 14 Jan 2016 17:53:04 +0000 From: One Thousand Gnomes To: Tom Herbert Cc: Haiyang Zhang , David Miller , "vkuznets@redhat.com" , "netdev@vger.kernel.org" , KY Srinivasan , "devel@linuxdriverproject.org" , "linux-kernel@vger.kernel.org" , "eric.dumazet@gmail.com" Subject: Re: [PATCH net-next] hv_netvsc: don't make assumptions on struct flow_keys layout Message-ID: <20160114175304.161ff0af@lxorguk.ukuu.org.uk> In-Reply-To: References: <1452159189-11473-1-git-send-email-vkuznets@redhat.com> <20160110.172558.367101858392871618.davem@davemloft.net> Organization: Intel Corporation X-Mailer: Claws Mail 3.12.0 (GTK+ 2.24.29; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > These results for Toeplitz are not plausible. Given random input you > cannot expect any hash function to produce such uniform results. I > suspect either your input data is biased or how your applying the hash > is. > > When I run 64 random IPv4 3-tuples through Toeplitz and Jenkins I get > something more reasonable: IPv4 address patterns are not random. Nothing like it. A long long time ago we did do a bunch of tuning for network hashes using big porn site data sets. Random it was not. It's probably hard to repeat that exercise now with geo specific routing, and all the front end caches and redirectors on big sites but I'd strongly suggest random input is not a good test, and also that you need to worry more about hash attacks than perfect distributions. Alan