From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7327C19CCED for ; Tue, 27 Aug 2024 13:03:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724763842; cv=none; b=VaSz1wZYTPLLBQna7/Kj+zh+w+CXvQr7RK7VPiTycIfoYigGmloapo1KkElb5vsQhhAwAksiB7zKxHDSt3X8hh5KnHJFg2z0amdMfzx80xN8qT7nrpQTomD73DprFhit/c+HU8TaJt7ITFQ65dqPMgGRXIM5GHSVtZJBeSHXP/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1724763842; c=relaxed/simple; bh=vAaaZtMp9WuQ5mW3vfQRnnthO9IqPaBGhvatGQ4RRjM=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=LXRQdCejFH0KnnHfh/kBBHGeNVSHvYuW3wZITU5PeYg95W2c5ZA8yV37qxL9TmlymH6GpzJ5JKfqOh9G3f1AjiBQZ6cWa8V9xAV11l5T/8NVd4v91iYRjtH3nW6N6o4OJXEBDa4DfrxUTtfiIMDUMlPL+YuKNcrQv74pQ+qsFzA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=hisilicon.com; spf=pass smtp.mailfrom=hisilicon.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=hisilicon.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=hisilicon.com Received: from mail.maildlp.com (unknown [172.19.163.44]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4WtSR63PmCz2CnX0; Tue, 27 Aug 2024 21:03:46 +0800 (CST) Received: from dggpeml500019.china.huawei.com (unknown [7.185.36.137]) by mail.maildlp.com (Postfix) with ESMTPS id 9E205140136; Tue, 27 Aug 2024 21:03:56 +0800 (CST) Received: from [10.67.121.58] (10.67.121.58) by dggpeml500019.china.huawei.com (7.185.36.137) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.1.2507.39; Tue, 27 Aug 2024 21:03:56 +0800 Message-ID: <643df4d5-ad44-f84a-6b15-614876d3cd2d@hisilicon.com> Date: Tue, 27 Aug 2024 21:03:56 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.3.2 Subject: Re: [PATCH v6 0/4] Add support for AArch64 AMUv1-based arch_freq_get_on_cpu To: Beata Michalska CC: Catalin Marinas , , , , , , , , , , , , References: <20240603082154.3830591-1-beata.michalska@arm.com> <8500d58c-e6c5-04c7-73a0-38d3f77f2cb7@hisilicon.com> From: Jie Zhan In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To dggpeml500019.china.huawei.com (7.185.36.137) On 26/08/2024 15:24, Beata Michalska wrote: > ... >> Hi Beata, > Hi Jie, >> I've recently tested this patchset on a Kunpeng system. >> It works as expected when reading scaling_cur_freq. >> The frequency samples are much stabler than what cppc_cpufreq returns. > Thank you for giving it a spin. > (and apologies for late reply) >> A few minor things. >> >> 1. I observed larger errors on idle cpus than busy cpus, though it's just up >> to 1%. >> Not sure if this comes from the uncertain time interval between the last >> tick and entering idle. >> The shorter averaging interval, the larger error, I supposed. > All right - will look into it. > Just for my benefit: that diff is strictly between arch_freq_avg_get_on_cpu > and cpufreq_driver->get(policy->cpu) ? I can't say whether it's "strictly" between them or not because driver->get() shows a fluctuating value. On my platform, cppc_cpufreq's driver->get() sometimes shows large errors on busy cpus (as reported by recent emails), but quite accurate on idle cpus (<1%). With this patch, the "error" on idle cpus as mentioned above is typically <1%, hence better in general. >> 2. In the current implementation, the resolution of frequency would be: >> max_freq_khz / SCHED_CAPACITY_SCALE >> This looks a bit unnecessary to me. >> >> It's supposed to get a better resolution if we can do this in >> arch_freq_get_on_cpu(): >> >> freq = delta_cycle_cnt * max_freq_khz / delta_const_cnt >> >> which may require caching both current and previous sets of counts in the >> per-cpu struct amu_cntr_sample. >> > arch_freq_get_on_cpu relies on the frequency scale factor to derive the average > frequency. The scale factor is being calculated based on the deltas you have > mentioned and arch_max_freq_scale which uses SCHED_CAPACITY_SCALE*2 factor to > accommodate for rather low reference frequencies. arch_freq_get_on_cpu just does > somewhat reverse computation to that. Yeah I understood this. arch_freq_get_on_cpu() now returns: freq = (arch_scale_freq_capacity() * arch_scale_freq_ref()) >> SCHED_CAPACITY_SHIFT The frequency resolution is (arch_scale_freq_ref() >> SCHED_CAPACITY_SHIFT), which is equivalent to max_freq_khz / SCHED_CAPACITY_SCALE. If we can directly do freq = delta_cycle_cnt * ref_freq_khz / delta_const_cnt in arch_freq_get_on_cpu(), it's supposed to have a 1KHz resolution. (sorry for the wrong multiplier in the last reply) Just similar to what's done in [1]. It could be more worthwhile to have a good resolution than utilising the arch_topology framework? [1] https://lore.kernel.org/all/20240229162520.970986-2-vanshikonda@os.amperecomputing.com/ > --- > BR > Beata >> Kind regards, >> Jie >>