From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 589EA2BB02 for ; Wed, 3 Apr 2024 21:34:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712180095; cv=none; b=Ha4ARlE/SoyR+QlvbmOrVaWltTMuo1KV8j/Jtn9IV+ifBBkDoLg/ekVXPbRNBCnZYmysTI7AYfOMsM+qLThMFCLz+5DioyloPnME1s6BktmVDj97evXLp3+PyibZSZOphpbwOdrc8kdP/JI/FPE/eqOnT4IZXpPaPCthIY5M49M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1712180095; c=relaxed/simple; bh=O/x3pR/Uq2m/RFQAAEF82MfnkT1toOKqKKJEqBr1+aM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=YPRqKmXUYloYnBQaeF7FMpwKjvmvdZOYfnPxz0SERgPWI7H1m7Eb4s8tclqRowhu4zj0vzS5CvSZO/0IGcWAkm4Im9KII90BZVDnEu3fmvBN8RDv+6oemZSEGuUIYcfZnWrbUc74lYyufJeUqP+7t4pSBFs9lCLVagaGkqoUyWw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 93FC21007; Wed, 3 Apr 2024 14:35:23 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CD68B3F7B4; Wed, 3 Apr 2024 14:34:49 -0700 (PDT) Date: Wed, 3 Apr 2024 23:34:49 +0200 From: Beata Michalska To: Vanshidhar Konda Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, ionela.voinescu@arm.com, sudeep.holla@arm.com, will@kernel.org, catalin.marinas@arm.com, vincent.guittot@linaro.org, sumitg@nvidia.com, yang@os.amperecomputing.com, lihuisong@huawei.com Subject: Re: [PATCH v3 0/3] Add support for AArch64 AMUv1-based arch_freq_get_on_cpu Message-ID: References: <20240312083431.3239989-1-beata.michalska@arm.com> <5bdlm4kzni6x2bdy7kmmomf7cmyohjhr4nr7v2mb2pchuhkulj@moakmpptnbg5> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5bdlm4kzni6x2bdy7kmmomf7cmyohjhr4nr7v2mb2pchuhkulj@moakmpptnbg5> On Mon, Mar 25, 2024 at 09:10:26AM -0700, Vanshidhar Konda wrote: > On Tue, Mar 12, 2024 at 08:34:28AM +0000, Beata Michalska wrote: > > Introducing arm64 specific version of arch_freq_get_on_cpu, cashing on > > existing implementation for FIE and AMUv1 support: the frequency scale > > factor, updated on each sched tick, serves as a base for retrieving > > the frequency for a given CPU, representing an average frequency > > reported between the ticks - thus its accuracy is limited. > > > > The changes have been rather lightly (due to some limitations) tested on > > an FVP model. > > > > I tested these changes on an Ampere system. The results from reading > scaling_cur_freq look reasonable in the majority of cases I tested. I > only saw some unexpected behavior with cores that were configured for > no_hz full. > > I observed the unexplained behavior when I tested as follows: > 1. Run stress on all cores > stress-ng --cpu 186 --timeout 10m --metrics-brief > 2. Observe scaling_cur_freq and cpuinfo_cur_freq for all cores > scaling_cur_freq values were within a few % of cpuinfo_cur_freq > 3. Kill stress test > 4. Observe scaling_cur_freq and cpuinfo_cur_freq for all cores > scaling_cur_freq values were within a few % of cpuinfo_cur_freq for > most cores except the ones configured with no_hz full. > > no_hz full = 122-127 > core scaling_cur_freq cpuinfo_cur_freq > [122]: 2997070 1000000 > [123]: 2997070 1000000 > [124]: 3000038 1000000 > [125]: 2997070 1000000 > [126]: 2997070 1000000 > [127]: 2997070 1000000 > > These values were reflected for multiple seconds. I suspect the cores > entered WFI and there was no update to the scale while those cores were > idle. > Right, so the problem is with updating the counters upon entering idle, which at this point is being done for all CPUs, and it should exclude the full dynticks ones - otherwise it leads to such bad readings. So for nohz_full cores cpufreq driver will have to take care of getting the current frequency. Will be sending a fix for that. Thank you very much for testing - appreciate that! --- BR Beata > Thanks, > Vanshi