From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752512AbcHKSQB (ORCPT ); Thu, 11 Aug 2016 14:16:01 -0400 Received: from mail-it0-f42.google.com ([209.85.214.42]:37787 "EHLO mail-it0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751088AbcHKSP7 (ORCPT ); Thu, 11 Aug 2016 14:15:59 -0400 Reply-To: ahs3@redhat.com Subject: Re: [PATCH v5] Force cppc_cpufreq to report values in KHz to fix user space reporting References: <1469049004-19069-1-git-send-email-ahs3@redhat.com> <20160801203156.GV4605@ubuntu> To: Viresh Kumar , ashwinch@google.com Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Prashanth Prakash From: Al Stone Organization: Red Hat, Inc. Message-ID: <872a4dd4-a752-507b-e720-ec2e6003bd8c@redhat.com> Date: Thu, 11 Aug 2016 12:15:56 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <20160801203156.GV4605@ubuntu> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/01/2016 02:31 PM, Viresh Kumar wrote: > [+ Ashwin's new email id..] > > On 20-07-16, 15:10, Al Stone wrote: >> When CPPC is being used by ACPI on arm64, user space tools such as >> cpupower report CPU frequency values from sysfs that are incorrect. >> >> What the driver was doing was reporting the values given by ACPI tables >> in whatever scale was used to provide them. However, the ACPI spec >> defines the CPPC values as unitless abstract numbers. Internal kernel >> structures such as struct perf_cap, in contrast, expect these values >> to be in KHz. When these struct values get reported via sysfs, the >> user space tools also assume they are in KHz, causing them to report >> incorrect values (for example, reporting a CPU frequency of 1MHz when >> it should be 1.8GHz). >> >> The downside is that this approach has some assumptions: >> >> (1) It relies on SMBIOS3 being used, *and* that the Max Frequency >> value for a processor is set to a non-zero value. >> >> (2) It assumes that all processors run at the same speed, or that >> the CPPC values have all been scaled to reflect relative speed. >> This patch retrieves the largest CPU Max Frequency from a type 4 DMI >> record that it can find. This may not be an issue, however, as a >> sampling of DMI data on x86 and arm64 indicates there is often only >> one such record regardless. Since CPPC is relatively new, it is >> unclear if the ACPI ASL will always be written to reflect any sort >> of relative performance of processors of differing speeds. >> >> (3) It assumes that performance and frequency both scale linearly. >> >> For arm64 servers, this may be sufficient, but it does rely on >> firmware values being set correctly. Hence, other approaches will >> be considered in the future. >> >> This has been tested on three arm64 servers, with and without DMI, with >> and without CPPC support. >> >> Changes for v5: >> -- Move code to cpufreq/cppc_cpufreq.c from acpi/cppc_acpi.c to keep >> frequency-related code together, and keep the CPPC abstract scale >> in ACPI (Prashanth Prakash) >> -- Fix the scaling to remove the incorrect assumption that frequency >> was always a range from zero to max; as a practical matter, it is >> not (Prasanth Prakash); this also allowed us to remove an over- >> engineered function to do this math. >> >> Changes for v4: >> -- Replaced magic constants with #defines (Rafael Wysocki) >> -- Renamed cppc_unitless_to_khz() to cppc_to_khz() (Rafael Wysocki) >> -- Replaced hidden initialization with a clearer form (Rafael Wysocki) >> -- Instead of picking up the first Max Speed value from DMI, we will >> now get the largest Max Speed; still an approximation, but slightly >> less subject to error (Rafael Wysocki) >> -- Kconfig for cppc_cpufreq now depends on DMI, instead of selecting >> it, in order to make sure DMI is set up properly (Rafael Wysocki) >> >> Changes for v3: >> -- Added clarifying commentary re short-term vs long-term fix (Alexey >> Klimov) >> -- Added range checking code to ensure proper arithmetic occurs, >> especially no division by zero (Alexey Klimov) >> >> Changes for v2: >> -- Corrected thinko: needed to have DEPENDS on DMI in Kconfig.arm, >> not SELECT DMI (found by build daemon) >> >> Signed-off-by: Al Stone >> Signed-off-by: Prashanth Prakash >> --- >> drivers/cpufreq/cppc_cpufreq.c | 53 ++++++++++++++++++++++++++++++++++++++---- >> 1 file changed, 49 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c >> index 8882b8e..6debc18 100644 >> --- a/drivers/cpufreq/cppc_cpufreq.c >> +++ b/drivers/cpufreq/cppc_cpufreq.c >> @@ -19,10 +19,19 @@ >> #include >> #include >> #include >> +#include >> #include >> >> +#include >> + >> #include >> >> +/* Minimum struct length needed for the DMI processor entry we want */ >> +#define DMI_ENTRY_PROCESSOR_MIN_LENGTH 48 >> + >> +/* Offest in the DMI processor structure for the max frequency */ >> +#define DMI_PROCESSOR_MAX_SPEED 0x14 >> + >> /* >> * These structs contain information parsed from per CPU >> * ACPI _CPC structures. >> @@ -32,6 +41,39 @@ >> */ >> static struct cpudata **all_cpu_data; >> >> +/* Capture the max KHz from DMI */ >> +static u64 cppc_dmi_max_khz; >> + >> +/* Callback function used to retrieve the max frequency from DMI */ >> +static void cppc_find_dmi_mhz(const struct dmi_header *dm, void *private) >> +{ >> + const u8 *dmi_data = (const u8 *)dm; >> + u16 *mhz = (u16 *)private; >> + >> + if (dm->type == DMI_ENTRY_PROCESSOR && >> + dm->length >= DMI_ENTRY_PROCESSOR_MIN_LENGTH) { >> + u16 val = (u16)get_unaligned((const u16 *) >> + (dmi_data + DMI_PROCESSOR_MAX_SPEED)); >> + *mhz = val > *mhz ? val : *mhz; >> + } >> +} >> + >> +/* Look up the max frequency in DMI */ >> +static u64 cppc_get_dmi_max_khz(void) >> +{ >> + u16 mhz = 0; >> + >> + dmi_walk(cppc_find_dmi_mhz, &mhz); >> + >> + /* >> + * Real stupid fallback value, just in case there is no >> + * actual value set. >> + */ >> + mhz = mhz ? mhz : 1; >> + >> + return (1000 * mhz); >> +} >> + >> static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, >> unsigned int target_freq, >> unsigned int relation) >> @@ -42,7 +84,7 @@ static int cppc_cpufreq_set_target(struct cpufreq_policy *policy, >> >> cpu = all_cpu_data[policy->cpu]; >> >> - cpu->perf_ctrls.desired_perf = target_freq; >> + cpu->perf_ctrls.desired_perf = target_freq * policy->max / cppc_dmi_max_khz; >> freqs.old = policy->cur; >> freqs.new = target_freq; >> >> @@ -94,8 +136,10 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy) >> return ret; >> } >> >> - policy->min = cpu->perf_caps.lowest_perf; >> - policy->max = cpu->perf_caps.highest_perf; >> + cppc_dmi_max_khz = cppc_get_dmi_max_khz(); >> + >> + policy->min = cpu->perf_caps.lowest_perf * cppc_dmi_max_khz / cpu->perf_caps.highest_perf; >> + policy->max = cppc_dmi_max_khz; >> policy->cpuinfo.min_freq = policy->min; >> policy->cpuinfo.max_freq = policy->max; >> policy->shared_type = cpu->shared_type; >> @@ -112,7 +156,8 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy) >> cpu->cur_policy = policy; >> >> /* Set policy->cur to max now. The governors will adjust later. */ >> - policy->cur = cpu->perf_ctrls.desired_perf = cpu->perf_caps.highest_perf; >> + policy->cur = cppc_dmi_max_khz; >> + cpu->perf_ctrls.desired_perf = cpu->perf_caps.highest_perf; >> >> ret = cppc_set_perf(cpu_num, &cpu->perf_ctrls); >> if (ret) >> -- >> 2.7.4 > Another gentle ping -- any comments? Can this get pulled in now? Thanks. -- ciao, al ----------------------------------- Al Stone Software Engineer Red Hat, Inc. ahs3@redhat.com -----------------------------------