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=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 5DFB9C388F7 for ; Fri, 13 Nov 2020 12:30:09 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 DD29920797 for ; Fri, 13 Nov 2020 12:30:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="n73r2lwQ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD29920797 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=LuRViD7lqo4Q7zXujcW3ki6iILtlPZJQBWNOFCA28Hg=; b=n73r2lwQUfEb/3PYKyjMxMOL1 bVFw4/RN2i3eDa21sEiTwGhKzabZBYoFJGsEkAefgjI1z4fuK6x5ss4fbNsZdyvPvoOd1JtMycn7T fkKfmlnukji/ypr7z9tRVMWEfiLYf9BnevBv/BUTFKH65v+yb5YADa39w7o/nk4MjwWLpAe7UDt8e oZQMHwaHAla9WpNeAQc0t3kQ4mG4RjdXu6/6OkMiyU9VbwflEk5KnoyK/YJ7LzT45ohPfiFC5jM3Z Wy9dWXONqi1S+EfLvyz0fzyBphitXccBFjm3AvlVCL8xTZXPbxWZFHKBqMj8ZYySXkATCPnyMz9X0 ml/+w3cbQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kdYCM-0006yN-SA; Fri, 13 Nov 2020 12:29:02 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kdYCB-0006uB-4b for linux-arm-kernel@lists.infradead.org; Fri, 13 Nov 2020 12:28:52 +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 05147142F; Fri, 13 Nov 2020 04:28:48 -0800 (PST) Received: from localhost (unknown [10.1.198.32]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9A8343F6CF; Fri, 13 Nov 2020 04:28:47 -0800 (PST) Date: Fri, 13 Nov 2020 12:28:46 +0000 From: Ionela Voinescu To: Catalin Marinas Subject: Re: [PATCH v4 3/3] arm64: implement CPPC FFH support using AMUs Message-ID: <20201113122846.GA31212@arm.com> References: <20201106125334.21570-1-ionela.voinescu@arm.com> <20201106125334.21570-4-ionela.voinescu@arm.com> <20201112180045.GO29613@gaia> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201112180045.GO29613@gaia> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201113_072851_310109_03515D78 X-CRM114-Status: GOOD ( 16.54 ) 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: mark.rutland@arm.com, linux-kernel@vger.kernel.org, sudeep.holla@arm.com, will@kernel.org, morten.rasmussen@arm.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On Thursday 12 Nov 2020 at 18:00:46 (+0000), Catalin Marinas wrote: > On Fri, Nov 06, 2020 at 12:53:34PM +0000, Ionela Voinescu wrote: > > +static inline > > +int counters_read_on_cpu(int cpu, smp_call_func_t func, u64 *val) > > +{ > > + if (!cpu_has_amu_feat(cpu)) > > + return -EOPNOTSUPP; > > + > > + smp_call_function_single(cpu, func, val, 1); > > + > > + return 0; > > +} > > I got lost in the cpufreq call chains. Can this function ever be called > with interrupts disabled? > The short answer is: not with the current implementation of its only user, the cppc_cpufreq driver (given the current cpufreq implementation). The long answer is: there is a case where the cpufreq .get function is called with local interrupts disabled - cpufreq_quick_get(), but there are a few "if"s in between this becoming a problem: 1. If cppc_cpufreq ever implements .setpolicy or, 1.1 Current implementation of cpufreq_quick_get() changes. 2. If one of the few users of cpufreq_quick_get() is used: cppc_cpufreq ends up being used as CPU cooling device(+IPA governor) or devfreq/tegra30 is used. In this potential case, smp_call_function_single() will warn us of call with irqs_disable() and if the stars align there could be a potential deadlock if two CPUs try to IPI (get counter reads of) each other. So it could be called with irqs disabled, but a few code changes are needed before that happens. I can bail out of counters_read_on_cpu() if irqs_disabled() to be on the safe side. Thanks for the review, Ionela. > -- > Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel