From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753440Ab1HKTjI (ORCPT ); Thu, 11 Aug 2011 15:39:08 -0400 Received: from merlin.infradead.org ([205.233.59.134]:47945 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753280Ab1HKTjG convert rfc822-to-8bit (ORCPT ); Thu, 11 Aug 2011 15:39:06 -0400 Subject: Re: [PATCH v2 0/2] new cpumask for hotpluggable CPUs From: Peter Zijlstra To: "Turquette, Mike" Cc: linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org, linaro-dev@lists.linaro.org, patches@linaro.org, gregkh@suse.de Date: Thu, 11 Aug 2011 21:38:39 +0200 In-Reply-To: References: <1313006614-28702-1-git-send-email-mturquette@ti.com> <1313087423.8491.11.camel@twins> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.0.2- Message-ID: <1313091519.8491.31.camel@twins> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-08-11 at 12:25 -0700, Turquette, Mike wrote: > On Thu, Aug 11, 2011 at 11:30 AM, Peter Zijlstra wrote: > > On Wed, 2011-08-10 at 13:03 -0700, Mike Turquette wrote: > >> This patch series introduces a new cpumask which tracks CPUs that > >> support hotplugging. The purpose of this patch series is to provide a > >> simple method for kernel code to know which CPUs can be hotplugged and > >> which ones cannot. Potential users of this code might be a thermal > >> mitigation technique which uses hotplug to lower temperature, or a power > >> capping mechanism which uses hotplug to lower power consumption. > >> > >> All the of usual cpumask helper functions are created for this new mask. > >> The second patch in this series simply sets the bit for elligible CPUs > >> while they are being registered. The cpumask itself is static after > >> boot and should not change (like the possbile mask). > > > > I still most strongly object to people using hotplug for these goals. > > > > Why do you need to go through the entire dance of hotplug just to idle a > > cpu? Hotplug not only idles the cpu but tears down (and rebuilds) an > > insane amount of resources associated with the cpu. > > I think you're nacking the wrong series. This patchset simply allows > kernel space to know which CPUs can go offline and which one can't, > which seems pretty innocuous. Are you fundamentally opposed to the > kernel having better accessor functions to this data? Yeah, people might think its sane to use it.. > I'll soon be posting some code which does implement hotplug as a > power-capping feature. I think *that* is the patch that you'll want > to nack. That too of course..