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=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 97CC7C433DF for ; Thu, 4 Jun 2020 01:32:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B40E20772 for ; Thu, 4 Jun 2020 01:32:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726970AbgFDBcx (ORCPT ); Wed, 3 Jun 2020 21:32:53 -0400 Received: from szxga07-in.huawei.com ([45.249.212.35]:52400 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725983AbgFDBcx (ORCPT ); Wed, 3 Jun 2020 21:32:53 -0400 Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 96913A50AD9BE0EBAFA8; Thu, 4 Jun 2020 09:32:51 +0800 (CST) Received: from [127.0.0.1] (10.166.215.101) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.487.0; Thu, 4 Jun 2020 09:32:42 +0800 Subject: Re: [Question]: about 'cpuinfo_cur_freq' shown in sysfs when the CPU is in idle state To: "Rafael J. Wysocki" , Viresh Kumar CC: "Rafael J. Wysocki" , Hanjun Guo , Sudeep Holla , Ionela Voinescu , Linux PM , "Linux Kernel Mailing List" References: <20200603075200.hbyofgcyiwocl565@vireshk-i7> From: Xiongfeng Wang Message-ID: <39d37e1b-7959-9a8f-6876-f2ed4c1dbc37@huawei.com> Date: Thu, 4 Jun 2020 09:32:41 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.166.215.101] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rafael, Thanks for your reply ! On 2020/6/3 21:39, Rafael J. Wysocki wrote: > On Wed, Jun 3, 2020 at 9:52 AM Viresh Kumar wrote: >> >> On 02-06-20, 11:34, Xiongfeng Wang wrote: >>> Hi Viresh, >>> >>> Sorry to disturb you about another problem as follows. >>> >>> CPPC use the increment of Desired Performance counter and Reference Performance >>> counter to get the CPU frequency and show it in sysfs through >>> 'cpuinfo_cur_freq'. But ACPI CPPC doesn't specifically define the behavior of >>> these two counters when the CPU is in idle state, such as stop incrementing when >>> the CPU is in idle state. >>> >>> ARMv8.4 Extension inctroduced support for the Activity Monitors Unit (AMU). The >>> processor frequency cycles and constant frequency cycles in AMU can be used as >>> Delivered Performance counter and Reference Performance counter. These two >>> counter in AMU does not increase when the PE is in WFI or WFE. So the increment >>> is zero when the PE is in WFI/WFE. This cause no issue because >>> 'cppc_get_rate_from_fbctrs()' in cppc_cpufreq driver will check the increment >>> and return the desired performance if the increment is zero. >>> >>> But when the CPU goes into power down idle state, accessing these two counters >>> in AMU by memory-mapped address will return zero. Such as CPU1 went into power >>> down idle state and CPU0 try to get the frequency of CPU1. In this situation, >>> will display a very big value for 'cpuinfo_cur_freq' in sysfs. Do you have some >>> advice about this problem ? >>> >>> I was thinking about an idea as follows. We can run 'cppc_cpufreq_get_rate()' on >>> the CPU to be measured, so that we can make sure the CPU is in C0 state when we >>> access the two counters. Also we can return the actual frequency rather than >>> desired performance when the CPU is in WFI/WFE. But this modification will >>> change the existing logical and I am not sure if this will cause some bad effect. >>> >>> >>> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c >>> index 257d726..ded3bcc 100644 >>> --- a/drivers/cpufreq/cppc_cpufreq.c >>> +++ b/drivers/cpufreq/cppc_cpufreq.c >>> @@ -396,9 +396,10 @@ static int cppc_get_rate_from_fbctrs(struct cppc_cpudata *cpu, >>> return cppc_cpufreq_perf_to_khz(cpu, delivered_perf); >>> } >>> >>> -static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) >>> +static int cppc_cpufreq_get_rate_cpu(void *info) >>> { >>> struct cppc_perf_fb_ctrs fb_ctrs_t0 = {0}, fb_ctrs_t1 = {0}; >>> + unsigned int cpunum = *(unsigned int *)info; >>> struct cppc_cpudata *cpu = all_cpu_data[cpunum]; >>> int ret; >>> >>> @@ -418,6 +419,22 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) >>> return cppc_get_rate_from_fbctrs(cpu, fb_ctrs_t0, fb_ctrs_t1); >>> } >>> >>> +static unsigned int cppc_cpufreq_get_rate(unsigned int cpunum) >>> +{ >>> + unsigned int ret; >>> + >>> + ret = smp_call_on_cpu(cpunum, cppc_cpufreq_get_rate_cpu, &cpunum, true); >>> + >>> + /* >>> + * convert negative error code to zero, otherwise we will display >>> + * an odd value for 'cpuinfo_cur_freq' in sysfs >>> + */ >>> + if (ret < 0) >>> + ret = 0; >>> + >>> + return ret; >>> +} >>> + >>> static int cppc_cpufreq_set_boost(struct cpufreq_policy *policy, int state) >>> { >>> struct cppc_cpudata *cpudata; >> >> I don't see any other sane solution, even if this brings the CPU back >> to normal state and waste power. We should be able to reliably provide >> value to userspace. >> >> Rafael / Sudeep: What you do say ? > > The frequency value obtained by kicking the CPU out of idle > artificially is bogus, though. You may as well return a random number > instead. Yes, it may return a randowm number as well. > > The frequency of a CPU in an idle state is in fact unknown in the case > at hand, so returning 0 looks like the cleanest option to me. I am not sure about how the user will use 'cpuinfo_cur_freq' in sysfs. If I return 0 when the CPU is idle, when I run a light load on the CPU, I will get a zero value for 'cpuinfo_cur_freq' when the CPU is idle. When the CPU is not idle, I will get a non-zero value. The user may feel odd about 'cpuinfo_cur_frreq' switching between a zero value and a non-zero value. They may hope it can return the frequency when the CPU execute instructions, namely in C0 state. I am not so sure about the user will look at 'cpuinfo_cur_freq'. Thanks, Xiongfeng > > Thanks! > > . >