From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: High contention on the sk_buff_head.lock Date: Wed, 18 Mar 2009 14:38:44 -0700 (PDT) Message-ID: <20090318.143844.173112261.davem@davemloft.net> References: <87prge1rhu.fsf@basil.nowhere.org> <20090318.140340.55290859.davem@davemloft.net> <49C16349.9030503@us.ibm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: andi@firstfloor.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org To: vernux@us.ibm.com Return-path: Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:46258 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751644AbZCRVi6 (ORCPT ); Wed, 18 Mar 2009 17:38:58 -0400 In-Reply-To: <49C16349.9030503@us.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Vernon Mauery Date: Wed, 18 Mar 2009 14:10:33 -0700 > David Miller wrote: > > From: Andi Kleen > > Date: Wed, 18 Mar 2009 21:54:37 +0100 > > > >> But then again I'm not sure it's worth it if the problem only > >> happens in out of tree RT. > > The list of problems that only show up with the RT kernel seems to be > > constantly increasing, but honestly is very surprising to me. > > I don't understand why we even need to be concerned about this stuff > > upstream, to be honest. > > Please reproduce this in the vanilla kernel, then get back to us. > > Huh? The numbers that I posted *were* from the vanilla kernel. I ran > the 2.6.29-rc8 kernel with lock_stat enabled. The lock contention > happens on the same lock in both vanilla and -rt, it just happens > to be more pronounced in the -rt kernel because of the double context > switches that the sleeping spinlock/rt-mutexes introduce. And the double context switches are probably also why less natural batching and locality are achieved in the RT kernel. Isn't that true?