From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: Linux Route Cache performance tests Date: Mon, 7 Nov 2011 13:42:44 +0000 Message-ID: <1320673364.3020.21.camel@bwh-desktop> References: <4EB6AE62.5050803@itcare.pl> <1320600597.6506.7.camel@edumazet-laptop> <4EB6D1D8.8040604@itcare.pl> <1320605326.6506.27.camel@edumazet-laptop> <4EB6DE06.7050009@itcare.pl> <1320608290.6506.33.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: =?UTF-8?Q?Pawe=C5=82?= Staszewski , Linux Network Development list To: Eric Dumazet Return-path: Received: from exchange.solarflare.com ([216.237.3.220]:18826 "EHLO exchange.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754394Ab1KGNmt (ORCPT ); Mon, 7 Nov 2011 08:42:49 -0500 In-Reply-To: <1320608290.6506.33.camel@edumazet-laptop> Sender: netdev-owner@vger.kernel.org List-ID: On Sun, 2011-11-06 at 20:38 +0100, Eric Dumazet wrote: > Le dimanche 06 novembre 2011 =C3=A0 20:20 +0100, Pawe=C5=82 Staszewsk= i a =C3=A9crit : [...] > > So the point of this test was figure out how much of route cache en= tries=20 > > Linux can handle without dropping performance. >=20 > No need to even do a bench, its pretty easy to understand how a hash > table is handled. >=20 > Allowing long chains is not good. >=20 > With your 512k slots hash table, you cannot expect handling 1.4M rout= es > with optimal performance. End of story. >=20 > Since route hash table is allocated at boot time, only way to change = its > size is using "rhash_entries=3D2097152" boot parameter. >=20 > If it still doesnt fly, try with "rhash_entries=3D4194304" A routing cache this big is not going to fit in the processor caches, anyway; in fact even the hash table may not. So a routing cache hit is likely to involve processor cache misses. After David's work to make cacheless operation faster, I suspect that such a 'hit' can be a net loss. But it *is* necessary to run a benchmark to answer this (and the answer will obviously vary between systems). Ben. --=20 Ben Hutchings, Staff Engineer, Solarflare Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.