From patchwork Thu Sep 4 09:10:00 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: preeti X-Patchwork-Id: 4843381 Return-Path: X-Original-To: patchwork-linux-pm@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork1.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork1.web.kernel.org (Postfix) with ESMTP id 23ED99F314 for ; Thu, 4 Sep 2014 09:11:05 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 1C4A7201B9 for ; Thu, 4 Sep 2014 09:11:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 898EA2011E for ; Thu, 4 Sep 2014 09:11:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754856AbaIDJKM (ORCPT ); Thu, 4 Sep 2014 05:10:12 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:39989 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755014AbaIDJKJ (ORCPT ); Thu, 4 Sep 2014 05:10:09 -0400 Received: from /spool/local by e8.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; Thu, 4 Sep 2014 05:10:06 -0400 Received: from b01cxnp23032.gho.pok.ibm.com (b01cxnp23032.gho.pok.ibm.com [9.57.198.27]) by d01dlp01.pok.ibm.com (Postfix) with ESMTP id EB9E138C803D; Thu, 4 Sep 2014 05:10:05 -0400 (EDT) Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id s849A5dH64028908; Thu, 4 Sep 2014 09:10:05 GMT Received: from d01av01.pok.ibm.com (localhost [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id s849A4sv003620; Thu, 4 Sep 2014 05:10:05 -0400 Received: from preeti.in.ibm.com (preeti.in.ibm.com [9.124.41.120] (may be forged)) by d01av01.pok.ibm.com (8.14.4/8.14.4/NCO v10.0 AVin) with ESMTP id s849A1tW003349; Thu, 4 Sep 2014 05:10:02 -0400 Message-ID: <54082C68.8030400@linux.vnet.ibm.com> Date: Thu, 04 Sep 2014 14:40:00 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Viresh Kumar , "Rafael J. Wysocki" , Dirk Brandewie , Dirk Brandewie CC: Linux PM list , "linux-kernel@vger.kernel.org" , Patrick Marlier Subject: Re: [PATCH 0/2] Add exit_prepare callback to the cpufreq_driver interface. References: <1394732168-12638-1-git-send-email-dirk.j.brandewie@intel.com> <53296AD0.5090908@linux.vnet.ibm.com> <19131121.D211TBerqb@vostro.rjw.lan> In-Reply-To: X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14090409-0320-0000-0000-00000064A410 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Spam-Status: No, score=-8.5 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP Hi, I went through the cpufreq code and the previous discussion in the context of this patch and I propose the below patch. Please let me know if it misses something that you all had discussed. On 09/04/2014 11:38 AM, Viresh Kumar wrote: > On 19 March 2014 19:49, Rafael J. Wysocki wrote: > >> That said, for the intel_pstate case ->stop() as proposed by Dirk is demonstrably >> sufficient and there are no other ->setpolicy drivers in sight wanting or needing >> anything else. >> >> So to me, (1) the new ->stop() should *only* be called for ->setpolicy drivers, >> because the purpose of it should be to "allow ->setpolicy drivers to do what the >> GOV_STOP will do for regular drivers" as you put it above, and (2) some code in >> the original intel_pstate's ->exit() may/should stay in there (instead of being >> moved to the new ->stop()), which is the only possibly remaining issue here. >> >> The whole discussion about possibly re-using ->stop() for ->target drivers goes >> in a totally wrong direction, because *if* ->target drivers need a new callback >> to be executed around where ->stop() is called for ->setpolicy drivers, *then* >> that has to be a *different* callback. >> >> And by the way, ->get() in fact has a different meaning for ->setpolicy drivers, >> so it would be good to consider logical separation of ->setpolicy and ->target >> drivers so that each kind has its own separate set of callbacks with no overlaps. >> That would make it easier to avoid breakage resulting from changes made with >> ->setpolicy drivers that also affect ->target drivers in unpredictable ways and >> the other way around. > > Okay, I have picked up a very old thread but it looks more sensible to start > replying here.. > > Preeti (Cc'd) wants to do something similar, i.e. reduce freq of a > core before it > goes down. And the driver is probably: drivers/cpufreq/powernv-cpufreq.c, which > is ->target() type. > > Now should we reuse the same callback ->stop_cpu() or implement a new one? > I don't know if adding a new callback would be a good idea here.. > > -- > viresh > cpufreq: Allow stop CPU callback to be used by all cpufreq drivers Commit 367dc4aa introduced the stop CPU callback for intel_pstate drivers. During the CPU_DOWN_PREPARE stage, this callback is invoked so that drivers can take some action on the pstate of the cpu before it is taken offline. This callback was assumed to be useful only for those drivers which have implemented the set_policy CPU callback because they have no other way to take action about the cpufreq of a CPU which is being hotplugged out except in the exit callback which is called very late in the offline process. The drivers which implement the target/target_index callbacks were expected to take care of requirements like the ones that commit 367dc4aa addresses in the GOV_STOP notification event. But there are disadvantages to restricting the usage of stop CPU callback to cpufreq drivers that implement the set_policy callbacks and who want to take explicit action on the setting the cpufreq during a hotplug operation. 1.GOV_STOP gets called for every CPU offline and drivers would usually want to take action when the last cpu in the policy->cpus mask is taken offline. As long as there is more than one cpu in the policy->cpus mask, cpufreq core itself makes sure that the freq for the other cpus in this mask is set according to the maximum load. This is sensible and drivers which implement the target_index callback would mostly not want to modify that. However the cpufreq core leaves a loose end when the cpu in the policy->cpus mask is the last one to go offline; it does nothing explicit to the frequency of the core. Drivers may need a way to take some action here and stop CPU callback mechanism is the best way to do it today. 2.We cannot implement driver specific actions in the GOV_STOP mechanism. So we will need another driver callback which is invoked from here which is unnecessary. Therefore this patch extends the usage of stop CPU callback to be used by all cpufreq drivers as long as they have this callback implemented and irrespective of whether they are set_policy/target_index drivers. The assumption is if the drivers find the GOV_STOP path to be a suitable way of implementing what they want to do with the freq of the cpu going offine,they will not implement the stop CPU callback at all. Signed-off-by: Preeti U Murthy --- To unsubscribe from this list: send the line "unsubscribe linux-pm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c index d9fdedd..6463f35 100644 --- a/drivers/cpufreq/cpufreq.c +++ b/drivers/cpufreq/cpufreq.c @@ -1380,7 +1380,7 @@ static int __cpufreq_remove_dev_prepare(struct device *dev, if (!cpufreq_suspended) pr_debug("%s: policy Kobject moved to cpu: %d from: %d\n", __func__, new_cpu, cpu); - } else if (cpufreq_driver->stop_cpu && cpufreq_driver->setpolicy) { + } else if (cpufreq_driver->stop_cpu) { cpufreq_driver->stop_cpu(policy); }