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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7AA8BC433EF for ; Tue, 15 Mar 2022 02:30:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344442AbiCOCbi (ORCPT ); Mon, 14 Mar 2022 22:31:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344432AbiCOCbh (ORCPT ); Mon, 14 Mar 2022 22:31:37 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 957AB47079; Mon, 14 Mar 2022 19:30:26 -0700 (PDT) Received: from canpemm500006.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KHcjT0DVNz9snV; Tue, 15 Mar 2022 10:26:37 +0800 (CST) Received: from [10.67.109.61] (10.67.109.61) by canpemm500006.china.huawei.com (7.192.105.130) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Tue, 15 Mar 2022 10:30:24 +0800 Subject: Re: [PATCH] cpufreq: fix cpufreq_get() can't get correct CPU frequency To: "Rafael J. Wysocki" References: <20220311081111.159639-1-zhengzucheng@huawei.com> CC: Viresh Kumar , Thomas Gleixner , Len Brown , Linux PM , Linux Kernel Mailing List , Stable From: zhengzucheng Message-ID: <100a5228-a941-0ff7-8133-14273472b6f5@huawei.com> Date: Tue, 15 Mar 2022 10:30:23 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.67.109.61] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To canpemm500006.china.huawei.com (7.192.105.130) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 2022/3/11 23:52, Rafael J. Wysocki wrote: > On Fri, Mar 11, 2022 at 9:11 AM z00314508 wrote: >> From: Zucheng Zheng >> >> On some specific platforms, the cpufreq driver does not define >> cpufreq_driver.get() routine (eg:x86 intel_pstate driver), as a > I guess you mean the cpufreq driver ->get callback. > > No, intel_pstate doesn't implement it, because it cannot reliably > return the current CPU frequency. > >> result, the cpufreq_get() can't get the correct CPU frequency. > No, it can't, if intel_pstate is the driver, but what's the problem? > This function is only called in one place in the kernel and not on x8 > even. > >> Modern x86 processors include the hardware needed to accurately >> calculate frequency over an interval -- APERF, MPERF and the TSC. > You can compute the average frequency over an interval, but ->get is > expected to return the actual current frequency at the time call time. > >> Here we use arch_freq_get_on_cpu() in preference to any driver >> driver-specific cpufreq_driver.get() routine to get CPU frequency. >> >> Fixes: f8475cef9008 ("x86: use common aperfmperf_khz_on_cpu() to calculate KHz using APERF/MPERF") > No kidding. > >> Signed-off-by: Zucheng Zheng >> --- >> drivers/cpufreq/cpufreq.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c >> index 80f535cc8a75..d777257b4454 100644 >> --- a/drivers/cpufreq/cpufreq.c >> +++ b/drivers/cpufreq/cpufreq.c >> @@ -1806,10 +1806,14 @@ unsigned int cpufreq_get(unsigned int cpu) >> { >> struct cpufreq_policy *policy = cpufreq_cpu_get(cpu); >> unsigned int ret_freq = 0; >> + unsigned int freq; >> >> if (policy) { >> down_read(&policy->rwsem); >> - if (cpufreq_driver->get) >> + freq = arch_freq_get_on_cpu(policy->cpu); >> + if (freq) >> + ret_freq = freq; >> + else if (cpufreq_driver->get) > Again, what problem exactly does this address? Thank you for review. In some scenarios, cpufreq driver ->get is not defined, some driver get the CPU frequency by calling cpufreq_get() will return 0. The modification to this problem is inspired by the implementation of the show_scaling_cur_freq(). > >> ret_freq = __cpufreq_get(policy); >> up_read(&policy->rwsem); >> >> -- > . >