From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB1B0C433E2 for ; Thu, 4 Jun 2020 07:12:17 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A7A2E206DC for ; Thu, 4 Jun 2020 07:12:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A7A2E206DC Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 7EFB36E297; Thu, 4 Jun 2020 07:11:46 +0000 (UTC) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by gabe.freedesktop.org (Postfix) with ESMTP id F406889DB5 for ; Wed, 3 Jun 2020 16:45:35 +0000 (UTC) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 5BF0255D; Wed, 3 Jun 2020 09:45:35 -0700 (PDT) Received: from [10.37.12.87] (unknown [10.37.12.87]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B64873F52E; Wed, 3 Jun 2020 09:45:24 -0700 (PDT) Subject: Re: [PATCH v8 4/8] PM / EM: add support for other devices than CPUs in Energy Model To: "Rafael J. Wysocki" References: <20200527095854.21714-1-lukasz.luba@arm.com> <20200527095854.21714-5-lukasz.luba@arm.com> <7201e161-6952-6e28-4036-bd0f0353ec30@arm.com> From: Lukasz Luba Message-ID: <6693c594-930b-b28e-58d0-f1b28b6eef58@arm.com> Date: Wed, 3 Jun 2020 17:45:22 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Mailman-Approved-At: Thu, 04 Jun 2020 07:11:42 +0000 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Nishanth Menon , Juri Lelli , Peter Zijlstra , Viresh Kumar , Liviu Dudau , dri-devel , Bjorn Andersson , Benjamin Segall , alyssa.rosenzweig@collabora.com, Matthias Kaehlcke , Amit Kucheria , Lorenzo Pieralisi , Vincent Guittot , Kevin Hilman , Andy Gross , Daniel Lezcano , steven.price@arm.com, Chanwoo Choi , Ingo Molnar , dl-linux-imx , "Zhang, Rui" , Mel Gorman , orjan.eide@arm.com, Linux PM , linux-arm-msm , Sascha Hauer , Steven Rostedt , "moderated list:ARM/Mediatek SoC..." , Matthias Brugger , Linux OMAP Mailing List , Dietmar Eggemann , Linux ARM , David Airlie , Tomeu Vizoso , Quentin Perret , Stephen Boyd , Randy Dunlap , "Rafael J. Wysocki" , Linux Kernel Mailing List , Bartlomiej Zolnierkiewicz , Sascha Hauer , Sudeep Holla , patrick.bellasi@matbug.net, Shawn Guo Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 6/3/20 5:22 PM, Rafael J. Wysocki wrote: > On Wed, Jun 3, 2020 at 6:12 PM Lukasz Luba wrote: >> >> >> >> On 6/3/20 4:40 PM, Rafael J. Wysocki wrote: >>> On Wed, Jun 3, 2020 at 5:26 PM Lukasz Luba wrote: >>>> >>>> >>>> >>>> On 6/3/20 4:13 PM, Rafael J. Wysocki wrote: >>>>> On Tue, Jun 2, 2020 at 1:31 PM Lukasz Luba wrote: >>>>>> >>>>>> Hi Daniel, >>>>>> >>>>>> On 6/1/20 10:44 PM, Daniel Lezcano wrote: >>>>>>> On 27/05/2020 11:58, Lukasz Luba wrote: >>>>>>>> Add support for other devices than CPUs. The registration function >>>>>>>> does not require a valid cpumask pointer and is ready to handle new >>>>>>>> devices. Some of the internal structures has been reorganized in order to >>>>>>>> keep consistent view (like removing per_cpu pd pointers). >>>>>>>> >>>>>>>> Signed-off-by: Lukasz Luba >>>>>>>> --- >>>>>>> >>>>>>> [ ... ] >>>>>>> >>>>>>>> } >>>>>>>> EXPORT_SYMBOL_GPL(em_register_perf_domain); >>>>>>>> + >>>>>>>> +/** >>>>>>>> + * em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for a device >>>>>>>> + * @dev : Device for which the EM is registered >>>>>>>> + * >>>>>>>> + * Try to unregister the EM for the specified device (but not a CPU). >>>>>>>> + */ >>>>>>>> +void em_dev_unregister_perf_domain(struct device *dev) >>>>>>>> +{ >>>>>>>> + if (IS_ERR_OR_NULL(dev) || !dev->em_pd) >>>>>>>> + return; >>>>>>>> + >>>>>>>> + if (_is_cpu_device(dev)) >>>>>>>> + return; >>>>>>>> + >>>>>>>> + mutex_lock(&em_pd_mutex); >>>>>>> >>>>>>> Is the mutex really needed? >>>>>> >>>>>> I just wanted to align this unregister code with register. Since there >>>>>> is debugfs dir lookup and the device's EM existence checks I thought it >>>>>> wouldn't harm just to lock for a while and make sure the registration >>>>>> path is not used. These two paths shouldn't affect each other, but with >>>>>> modules loading/unloading I wanted to play safe. >>>>>> >>>>>> I can change it maybe to just dmb() and the end of the function if it's >>>>>> a big performance problem in this unloading path. What do you think? >>>>> >>>>> I would rather leave the mutex locking as is. >>>>> >>>>> However, the question to ask is what exactly may go wrong without that >>>>> locking in place? Is there any specific race condition that you are >>>>> concerned about? >>>>> >>>> >>>> I tried to test this with module loading & unloading with panfrost >>>> driver and CPU hotplug (which should bail out quickly) and was OK. >>>> I don't see any particular race. I don't too much about the >>>> debugfs code, though. That's why I tried to protect from some >>>> scripts/services which try to re-load the driver. >>>> >>>> Apart from that, maybe just this dev->em = NULL to be populated to all >>>> CPUs, which mutex_unlock synchronizes for free here. >>> >>> If it may run concurrently with the registration for the same device, >>> the locking is necessary, but in that case the !dev->em_pd check needs >>> to go under the mutex too IMO, or you may end up leaking the pd if the >>> registration can run between that check and the point at which the >>> mutex is taken. >> >> They don't run concurrently for the same device and users of that EM are >> already gone. >> I just wanted to be sure that everything is cleaned and synced properly. >> Here is some example of the directories under >> /sys/kernel/debug/energy_model >> cpu0, cpu4, gpu, dsp, etc >> >> The only worry that I had was the debugfs dir name, which is a >> string from dev_name() and will be the same for the next registration >> if module is re-loaded. > > OK, so that needs to be explained in a comment. OK, I will add it. > >> So the 'name' is reused and debugfs_create_dir() >> and debugfs_remove_recursive() uses this fsnotify, but they are >> operating under inode_lock/unlock() on the parent dir 'energy_model'. >> Then there is also this debugfs_lookup() which is slightly different. >> >> That's why I put a mutex to separate all registration and unregistration >> for all devices. >> It should work without the mutex in unregister path, but I think it does >> not harm to take > > Well, fair enough, but I still think that the !dev->em_pd check should > be done under the mutex or it will be confusing. > >> it just in case and also have the CPU variable sync for free. > > I'm not sure what you mean by the last part here? The mutex_unlock for me also means dmb() took place. ARM has slightly different memory model than x86 and I just wanted to be sure that this new values reach memory and become visible to other cores. mutex_unlock just guaranties this for me. > >>> >>> Apart from this your kerneldoc comments might me improved IMO. >>> >>> First of all, you can use @dev inside of a kerneldoc (if @dev >>> represents an argument of the documented function) and that will >>> produce the right output automatically. >> >> OK >> >>> >>> Second, it is better to avoid saying things like "Try to unregister >>> ..." in kerneldoc comments (the "Try to" part is redundant). Simply >>> say "Unregister ..." instead. >> >> Good point, thanks, I will use "Unregister ..." then. >> >>> >>> Thanks! >>> >> >> Shell I send a 'resend patch' which changes these @dev and >> 'unregister' comments? > > Yes, please, but see the comments above too. Saw it > >> Or wait for you to finish reviewing the other patches and send v9? > > That is not necessary, unless you want to make kerneldoc improvements > in the other patches. I will check them, but if they are OKish then I will just resend this one. Thank you for the review. Regards, Lukasz _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel