From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753971Ab1ILSxx (ORCPT ); Mon, 12 Sep 2011 14:53:53 -0400 Received: from merlin.infradead.org ([205.233.59.134]:38285 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753639Ab1ILSxw convert rfc822-to-8bit (ORCPT ); Mon, 12 Sep 2011 14:53:52 -0400 Subject: Re: [PATCH 8/5] llist: Remove cpu_relax() usage in cmpxchg loops From: Peter Zijlstra To: Andi Kleen Cc: Mathieu Desnoyers , Huang Ying , Andrew Morton , linux-kernel@vger.kernel.org Date: Mon, 12 Sep 2011 20:53:28 +0200 In-Reply-To: <20110912163842.GO7761@one.firstfloor.org> References: <1315461646-1379-1-git-send-email-ying.huang@intel.com> <1315836358.26517.43.camel@twins> <20110912142305.GN7761@one.firstfloor.org> <20110912144706.GA21716@Krystal> <20110912163842.GO7761@one.firstfloor.org> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.3- Message-ID: <1315853608.575.1.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2011-09-12 at 18:38 +0200, Andi Kleen wrote: > > so basically, in typical locking primitives (spinlock), it looks like > > lower power consumption is preferred over getting the raw maximal > > It's not only power, its: > - Allow the other siblings make more progress on SMT > - Do some backoff to stress the interconnect less (this is important on >2S): > A tight loop which constantly writes is a extremly stressfull pattern. > - Save some power by allowing the CPU to do more clock gating If you're hitting a cmpxchg hard enough for any of those to make a difference you're doing it wrong.