From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH 3/7] idle, thermal, acpi: Remove home grown idle implementations Date: Thu, 21 Nov 2013 09:27:42 -0800 Message-ID: <20131121172742.GW4138@linux.vnet.ibm.com> References: <20131120160450.072555619@infradead.org> <20131120162736.508462614@infradead.org> <20131120165406.14fa0f09@ultegra> <20131121082151.GU10022@twins.programming.kicks-ass.net> <20131121160716.GT4138@linux.vnet.ibm.com> <20131121162956.GI10022@twins.programming.kicks-ass.net> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e39.co.us.ibm.com ([32.97.110.160]:54745 "EHLO e39.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751373Ab3KUR1r (ORCPT ); Thu, 21 Nov 2013 12:27:47 -0500 Received: from /spool/local by e39.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 21 Nov 2013 10:27:47 -0700 Content-Disposition: inline In-Reply-To: <20131121162956.GI10022@twins.programming.kicks-ass.net> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Peter Zijlstra Cc: Jacob Pan , Arjan van de Ven , lenb@kernel.org, rjw@rjwysocki.net, Eliezer Tamir , Chris Leech , David Miller , rui.zhang@intel.com, Mike Galbraith , Ingo Molnar , hpa@zytor.com, Thomas Gleixner , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "Rafael J. Wysocki" On Thu, Nov 21, 2013 at 05:29:56PM +0100, Peter Zijlstra wrote: > On Thu, Nov 21, 2013 at 08:07:16AM -0800, Paul E. McKenney wrote: > > On Thu, Nov 21, 2013 at 09:21:51AM +0100, Peter Zijlstra wrote: > > > On Wed, Nov 20, 2013 at 04:54:06PM -0800, Jacob Pan wrote: > > > > On Wed, 20 Nov 2013 17:04:53 +0100 > > > > Peter Zijlstra wrote: > > > > > > > > > People are starting to grow their own idle implementations in various > > > > > disgusting ways. Collapse the lot and use the generic idle code to > > > > > provide a proper idle cycle implementation. > > > > > > > > > +Paul > > > > > > > > RCU and others rely on is_idle_task() might be broken with the > > > > consolidated idle code since caller of do_idle may have pid != 0. > > > > > > > > Should we use TS_POLL or introduce a new flag to identify idle task? > > > > > > PF_IDLE would be my preference, I checked and we seem to have a grand > > > total of 2 unused task_struct::flags left ;-) > > > > As long as RCU has some reliable way to identify an idle task, I am > > good. But I have to ask -- why can't idle injection coordinate with > > the existing idle tasks rather than temporarily making alternative > > idle tasks? > > Because that'd completely wreck how the scheduler selects tasks for just > these 2 arguably insane drivers. > > We'd have to somehow teach it to pick the actual idle task instead of > this one task, but keep scheduling the rest of the tasks like normal -- > we very much should keep higher priority tasks running like normal. > > And we'd need a way to make it stop doing this 'proxy' execution. > > That said, once we manage to replace the entire PI implementation with a > proper proxy execution scheme, the above would be possible by having a > resource (rt_mutex) associated with every idle task, and always held by > that task. > > At that point we can do something like: > > rt_mutex_lock_timeout(cpu_idle_lock(cpu), jiffies); > > And get the idle thread executing in our stead. > > That said, idle is _special_ and I'd not be surprised we'd find a few > 'funnies' along the way of trying to get that to actually work. > > For now I'd rather not go there quite yet. Fair enough! Thanx, Paul