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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 549ABC352A4 for ; Wed, 12 Feb 2020 19:20:14 +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 2384E2082F for ; Wed, 12 Feb 2020 19:20:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="mLbaQG6t" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2384E2082F 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=nMSrgZwUZBPmaqXBcjM0kmoFcX/KJ7X1sm2wt48dl2Y=; b=mLbaQG6tGF3NcpE6RMtmIRJZE RXUrk6Gf7MaY+HCToiTfGzT9HDyPs/h5iI2wr+o/hbSvlskgzcn8SfuwKd82Ek3e8mcLViiQwyYoS PnsetQzIRN5yjsTSX8GYUvM6OObex1QfR5WZFkn8JfyWqgbXaItwGlH0xq5pzUU5ZUAIhbSj8pmIZ QQNs1jMu9YVIzUwEpr0HdrBxbv7uPJCe9JiaOwDoEfryrZvja/Xxlb2xSdamS4+hssailmualkYfR VyECfLu0mMeT6Y5wdCvS7UznYyc/wcguBPHaGvkAVV4lg2nSyQt94szZjr5tMpTnp8GPDDbPEqOpw S0WeEAsoA==; 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 1j1xYJ-0003wm-5e; Wed, 12 Feb 2020 19:20:03 +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 1j1xYF-0003tG-6T for linux-arm-kernel@lists.infradead.org; Wed, 12 Feb 2020 19:20:00 +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 D5ADE30E; Wed, 12 Feb 2020 11:19:56 -0800 (PST) Received: from [192.168.0.21] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 597093F68E; Wed, 12 Feb 2020 11:19:53 -0800 (PST) Subject: Re: [PATCH v3 1/7] arm64: add support for the AMU extension v1 To: Ionela.Voinescu@arm.com References: <20200211184542.29585-1-ionela.voinescu@arm.com> <20200211184542.29585-2-ionela.voinescu@arm.com> <93472f17-6465-641d-ea82-3230b5697ffd@arm.com> <20200212161045.GA7475@arm.com> <133890f7-59bb-63b9-0ca8-2294e3596058@arm.com> <20200212182008.GA25421@arm.com> From: Suzuki K Poulose Message-ID: Date: Wed, 12 Feb 2020 19:24:13 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200212182008.GA25421@arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200212_111959_327333_869FBEA0 X-CRM114-Status: GOOD ( 28.20 ) 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, maz@kernel.org, linux-doc@vger.kernel.org, peterz@infradead.org, catalin.marinas@arm.com, linux-pm@vger.kernel.org, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, mingo@redhat.com, viresh.kumar@linaro.org, linux-arm-kernel@lists.infradead.org, sudeep.holla@arm.com, will@kernel.org, valentin.schneider@arm.com, lukasz.luba@arm.com 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 Hi Ionela, On 02/12/2020 06:20 PM, Ionela Voinescu wrote: > Hi Suzuki, > > On Wednesday 12 Feb 2020 at 16:20:56 (+0000), Suzuki Kuruppassery Poulose wrote: >>>>> +static bool has_amu(const struct arm64_cpu_capabilities *cap, >>>>> + int __unused) >>>>> +{ >>>>> + /* >>>>> + * The AMU extension is a non-conflicting feature: the kernel can >>>>> + * safely run a mix of CPUs with and without support for the >>>>> + * activity monitors extension. Therefore, if not disabled through >>>>> + * the kernel command line early parameter, enable the capability >>>>> + * to allow any late CPU to use the feature. >>>>> + * >>>>> + * With this feature enabled, the cpu_enable function will be called >>>>> + * for all CPUs that match the criteria, including secondary and >>>>> + * hotplugged, marking this feature as present on that respective CPU. >>>>> + * The enable function will also print a detection message. >>>>> + */ >>>>> + >>>>> + if (!disable_amu && !zalloc_cpumask_var(&amu_cpus, GFP_KERNEL)) { >>>> >>>> This looks problematic. Don't we end up in allocating the memory during >>>> "each CPU" check and thus leaking memory ? Do we really need to allocate >>>> this dynamically ? >>>> >>> >>> Yes, it does make some assumptions. Given that the AMU capability is >>> a WEAK_LOCAL_CPU_FEATURE I relied on the match function being called >>> only once, when the return value is true. If the return value is false, >> >> That is not correct. A WEAK_LOCAL_CPU_FEATURE is still SCOPE_LOCAL_CPU, >> implies it is run on all the booting CPUs (including the hotplugged >> ones). The WEAK is there to imply that its "permitted" or "optional" >> for a hotplugged CPU. So, eventually you will re-allocate this variable >> every single time a CPU turns up, where you could also loose the current >> state. >> > >>> which will result in it being called multiple times, it's either because >>> disable_amu == false, or it has become false due to a previous failed >>> allocation, in which case a new allocation will not be attempted. > > First of all, I agree with you that this should be corrected. > > But for completion (and my education) I retraced my steps in regards > to my assumption above. While cpu_enable is called for all CPUs - boot, > secondary, hotplugged, the matches function (in this case has_amu) is > not always called for all CPUs, and that's where the confusion came > from. > > Looking over the update_cpu_capabilities function, that's called from > both setup_boot_cpu_capabilities and check_local_cpu_capabilities > (secondary CPUs) for SCOPE_LOCAL_CPU: > > ----- > static void update_cpu_capabilities(u16 scope_mask) > { > int i; > const struct arm64_cpu_capabilities *caps; > > scope_mask &= ARM64_CPUCAP_SCOPE_MASK; > for (i = 0; i < ARM64_NCAPS; i++) { > caps = cpu_hwcaps_ptrs[i]; > if (!caps || !(caps->type & scope_mask) || > cpus_have_cap(caps->capability) || > !caps->matches(caps, cpucap_default_scope(caps))) > continue; > > --> The matches function is only called if !cpus_have_cap Agreed. Your analysis is correct. This was done as a micro optimization(!) as it is pointless to check if something should be set, when it is already set. > > > if (caps->desc) > pr_info("detected: %s\n", caps->desc); > cpus_set_cap(caps->capability); > > --> If matches returns true we mark it as present in cpu_hwcaps. > > if ((scope_mask & SCOPE_BOOT_CPU) && (caps->type & SCOPE_BOOT_CPU)) > set_bit(caps->capability, boot_capabilities); > } > } > --- > > Therefore caps->matches (in this case has_amu) will only be called as > long as it returns false. This is where my assumption above came from. > Also, this is the reason it was working nicely in my testing, as I did > not test hotplug this time. > > Where the has_amu code breaks is when we end up calling > verify_local_cpu_capabilities instead of update_cpu_capabilities after > sys_caps_initialised, which will happen for hotplugged CPUs. > In that case we call caps->matches for all CPUs. Also, if anyone in the > future ends up calling this_cpu_has_cap for the AMU capability. True. > > I will fix this. Cheers Suzuki _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel