From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with ESMTP id B96A78D0039 for ; Tue, 1 Mar 2011 22:02:13 -0500 (EST) Received: by wyi11 with SMTP id 11so6831020wyi.14 for ; Tue, 01 Mar 2011 19:02:10 -0800 (PST) Subject: Re: [PATCH 4/4 V2] net,rcu: don't assume the size of struct rcu_head From: Eric Dumazet In-Reply-To: <4D6DAF86.2000407@cn.fujitsu.com> References: <4D6CA860.3020409@cn.fujitsu.com> <20110301.001638.104075130.davem@davemloft.net> <4D6CB414.8050107@cn.fujitsu.com> <1298971213.3284.4.camel@edumazet-laptop> <4D6DAF86.2000407@cn.fujitsu.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 02 Mar 2011 04:02:05 +0100 Message-ID: <1299034925.2930.52.camel@edumazet-laptop> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: Lai Jiangshan Cc: David Miller , mingo@elte.hu, paulmck@linux.vnet.ibm.com, cl@linux-foundation.org, penberg@kernel.org, mpm@selenic.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Le mercredi 02 mars 2011 A 10:46 +0800, Lai Jiangshan a A(C)crit : > Is it the cause of false sharing? I thought that all are rare write(except __refcnt) > since it is protected by RCU. > > Do you allow me just move the seldom access rcu_head to the end of the structure > and add pads before __refcnt? I guess it increases about 3% the size of dst_entry. dst_entry is a base class. Its included at the beginning of other structs. Moving rcu_head "at the end" just move it right in the middle of upper objects as a matter of fact. This might add one cache line miss on critical network object. A complete audit is needed. David is doing some changes in this area, so things move fast anyway. > I accept that I leave this code as is, when I change rcu_head I will notify you. > Thanks -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org