From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH 0/3] net: RCU lookups for UDP, DCCP and TCP protocol Date: Thu, 13 Nov 2008 18:20:09 +0100 Message-ID: <87k5b7czli.fsf@basil.nowhere.org> References: <4908627C.6030001@acm.org> <490874F2.2060306@cosmosbay.com> <49088288.6050805@acm.org> <49088AD1.7040805@cosmosbay.com> <20081029163739.GB6732@linux.vnet.ibm.com> <49089BE5.3090705@acm.org> <4908A134.4040705@cosmosbay.com> <4908AB3F.1060003@acm.org> <20081029185200.GE6732@linux.vnet.ibm.com> <4908C0CD.5050406@cosmosbay.com> <20081029201759.GF6732@linux.vnet.ibm.com> <4908DEDE.5030706@cosmosbay.com> <4909D551.9080309@cosmosbay.com> <491C27F0.8000507@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: David Miller , "Paul E. McKenney" , Corey Minyard , Stephen Hemminger , benny+usenet@amorsen.dk, Linux Netdev List , Christoph Lameter , Peter Zijlstra , Evgeniy Polyakov , Christian Bell To: Eric Dumazet Return-path: Received: from one.firstfloor.org ([213.235.205.2]:49207 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754023AbYKMRUM (ORCPT ); Thu, 13 Nov 2008 12:20:12 -0500 In-Reply-To: <491C27F0.8000507@cosmosbay.com> (Eric Dumazet's message of "Thu, 13 Nov 2008 14:13:20 +0100") Sender: netdev-owner@vger.kernel.org List-ID: Eric Dumazet writes: > 1) Introduce hlist_nulls variant of hlist > > hlist uses NULL value to finish a chain. > hlist_nulls variant use the low order bit set to 1 to signal an end marker. > This allows to store many different end markers, so that some RCU lockless > algos (used in TCP/UDP stack for example) can save some memory barriers in > fast paths. Do you have any numbers that demonstrate the read memory barriers being a performance problem? At least on x86 they should be very cheap because they're normally nops. -Andi -- ak@linux.intel.com