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=-5.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 50864C433E0 for ; Wed, 3 Jun 2020 15:26:10 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 1F8E0206A2 for ; Wed, 3 Jun 2020 15:26:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="gL/6KC4j" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1F8E0206A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=7yVJ63te1yEpb2Ix+gAbHawwsyrcf+mAt0zZ7eobY9Y=; b=gL/6KC4jq6vXuW9qIX+NapM0l fqNzrhsT7EdwA0SMSjL+iYf7Y5KWSxMGQjf8CCvwkyuKSWUE2INx1WhszuXtovHIX6e+JrTWRUB9T +mUunaOgaBxQNmVh1bs/+svJbfS7qTmWUxtVylc0F22C5bLnQlx/XFKg8n7T7s+/6+y5dgIbwg7Gt 58Urz6V7I5sNLvcGZ/lyas8rHRF2ZUruENjaHiB4HRYwJCmXnpBOwgd7zghN2I5n/lflK/g0J29T5 f3lnkTfzj+2bu3/F2pB9hZUxbS6MX3P/8JYjH/CAHF8+38jyza2MOqQp+kovvxqH4KD/D8AUjqn27 ldO6kC+/Q==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgVHM-0003kX-Oq; Wed, 03 Jun 2020 15:26:08 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgVHJ-0003jc-Ux; Wed, 03 Jun 2020 15:26:07 +0000 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 85D2A55D; Wed, 3 Jun 2020 08:26:02 -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 2A4FB3F52E; Wed, 3 Jun 2020 08:25:51 -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: Date: Wed, 3 Jun 2020 16:25:50 +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-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200603_082606_100312_E35CC15B X-CRM114-Status: GOOD ( 21.04 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: 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, Fabio Estevam , Matthias Kaehlcke , Rob Herring , Amit Kucheria , Lorenzo Pieralisi , 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, Daniel Vetter , 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" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. Regards, Lukasz _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel