From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754904Ab0CCQqv (ORCPT ); Wed, 3 Mar 2010 11:46:51 -0500 Received: from ms01.sssup.it ([193.205.80.99]:43726 "EHLO sssup.it" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754881Ab0CCQqs (ORCPT ); Wed, 3 Mar 2010 11:46:48 -0500 Date: Wed, 3 Mar 2010 17:59:26 +0100 From: Fabio Checconi To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , Paul Turner , Dario Faggioli , Michael Trimarchi , Dhaval Giani , Tommaso Cucinotta , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] sched: enforce per-cpu utilization limits on runtime balancing Message-ID: <20100303165926.GM2490@gandalf.sssup.it> References: <91b76b9b7555024d9afd7264eeae1b2db6a5e74c.1266931410.git.fabio@helm.retis> <1267129702.22519.558.camel@laptop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1267129702.22519.558.camel@laptop> User-Agent: Mutt/1.5.20 (2009-10-28) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > From: Peter Zijlstra > Date: Thu, Feb 25, 2010 09:28:22PM +0100 > > On Tue, 2010-02-23 at 19:56 +0100, Fabio Checconi wrote: > > + /* > > + * Make sure that before restarting balancing everyone > > + * sees the new free bandwidth. > > + */ > > + smp_wmb(); > > You cannot order something on its own, barriers come in pairs, where is > his? It was coupled with the acquire barrier implied by the spin_lock(rt_b) in the balance path, as the other wmb() before starting the reset (more details on the reply about this last barrier, as per your comment they can be removed).