Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751880AbdC0RSP (ORCPT ); Mon, 27 Mar 2017 13:18:15 -0400 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:53264 "EHLO cloudserver094114.home.net.pl" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751394AbdC0RSF (ORCPT ); Mon, 27 Mar 2017 13:18:05 -0400 From: "Rafael J. Wysocki" To: Juri Lelli Cc: Peter Zijlstra , mingo@redhat.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, tglx@linutronix.de, vincent.guittot@linaro.org, rostedt@goodmis.org, luca.abeni@santannapisa.it, claudio@evidence.eu.com, tommaso.cucinotta@santannapisa.it, bristot@redhat.com, mathieu.poirier@linaro.org, tkjos@android.com, joelaf@google.com, andresoportus@google.com, morten.rasmussen@arm.com, dietmar.eggemann@arm.com, patrick.bellasi@arm.com, Ingo Molnar , "Rafael J . Wysocki" , Mark Brown Subject: Re: [RFD PATCH 3/5] sched/cpufreq_schedutil: make worker kthread be SCHED_DEADLINE Date: Mon, 27 Mar 2017 19:05:06 +0200 Message-ID: <37277532.TseFq3j8HT@aspire.rjw.lan> User-Agent: KMail/4.14.10 (Linux/4.10.0+; KDE/4.14.9; x86_64; ; ) In-Reply-To: <20170327170134.GC10289@e106622-lin> References: <20170324140900.7334-1-juri.lelli@arm.com> <20170327165011.dpip23cyolnleas6@hirez.programming.kicks-ass.net> <20170327170134.GC10289@e106622-lin> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1648 Lines: 51 On Monday, March 27, 2017 06:01:34 PM Juri Lelli wrote: > On 27/03/17 18:50, Peter Zijlstra wrote: > > On Fri, Mar 24, 2017 at 02:08:58PM +0000, Juri Lelli wrote: > > > Worker kthread needs to be able to change frequency for all other > > > threads. > > > > > > Make it special, just under STOP class. > > > > *yuck* ;-) > > > > Eh, I know. :/ > > > So imagine our I2C/SPI bus is 'busy' and its mutex taken, then this > > 'soecial' task will need to boost it. Now add BWI to your thinking and > > shudder. > > > > Currently that kthread is FIFO already, so boosting still applies. Not as > bad as in the BWI case though. More thinking required. > > > > > On IRC broonie mentioned that: > > > > - most PMIC operations are fire and forget (no need to wait for a > > response). > > - PMIC 'packets' are 'small'. > > - SPI has the possibility to push stuff on the queue. > > > > Taken together this seems to suggest we can rework cpufreq drivers to > > function in-context, either directly push the packet on the bus if > > available, or queue it and let whoever owns it sort it without blocking. > > > > It might be possible to rework/augment I2C to also support pushing stuff > > on a queue. > > > > > > So if we can make all that work, we can do away with this horrible > > horrible kthread. Which is, IMO, a much better solution. > > > > Thoughts? > > Right. This is more a schedutil (cpufreq) problem though, IMHO. Even if > I agree that what you are proposing is way more clean (and here I > actually assume it's feasible at all), I fear it will take quite some > time to get reworked. Why do you think so? Thanks, Rafael