From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752412AbaLROnV (ORCPT ); Thu, 18 Dec 2014 09:43:21 -0500 Received: from www.linutronix.de ([62.245.132.108]:59065 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751057AbaLROnU (ORCPT ); Thu, 18 Dec 2014 09:43:20 -0500 Date: Thu, 18 Dec 2014 15:43:06 +0100 (CET) From: Thomas Gleixner To: Eduardo Valentin cc: Preeti Murthy , Preeti U Murthy , Viresh Kumar , Frederic Weisbecker , Fengguang Wu , Frederic Weisbecker , "Pan, Jacob jun" , LKML , LKP , Peter Zijlstra , Zhang Rui Subject: Re: [PATCH] tick/powerclamp: Remove tick_nohz_idle abuse In-Reply-To: <20141218140106.GA6323@developer> Message-ID: References: <20141218140106.GA6323@developer> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 18 Dec 2014, Eduardo Valentin wrote: > > The real solution is to fix the powerclamp driver by rewriting it with > > a sane concept, but that's beyond the scope of this. > > > > Do you have suggestions on what exactly is the expected rewriting or the > correct sane concepts? There was quite some discussion about this in this very thread. > > So the only solution for now is to remove the calls into the core NOHZ > > code from the powerclamp trainwreck along with the exports. > > > > Fixes: d6d71ee4a14a "PM: Introduce Intel PowerClamp Driver" > > If I got it right, the driver is currently broken due to changes in NOHZ > core. So, does this patch fix power clamp behavior ? The driver has been broken forever. It just worked by chance. Now a very well justified and correct change in the core code exposed that wreckage. So we have 2 choices: 1) Get rid of the abuse and let powerclamp deal with the problem. 2) Revert a correct patch for the sake of a 'works by chance' driver or put hacky workarounds in the core. Either of that will just paper over the real root cause until the next thing breaks in subtle ways. #1 is the only sane decision. We cannot deal with misdesigned driver code in the NOHZ core. > If I got your proposal right, in the end power clamp will be still > broken, but at least won't be abusing NOHZ. Is that what you are > proposing? Yes, the design of powerclamp stays broken, but the NOHZ abuse is gone. powerclamp will work, but it can't benefit from the possible longer idle times anymore. Thanks, tglx