On 09/13/2016 07:09 PM, Rafael J. Wysocki wrote: > On Wednesday, July 20, 2016 03:10:04 PM 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 <a...@redhat.com> >> Signed-off-by: Prashanth Prakash <pprak...@codeaurora.org> > > Applied. > > Thanks, > Rafael >
I've been on vacation so just now am seeing this. Thanks, Rafael! -- ciao, al ----------------------------------- Al Stone Software Engineer Red Hat, Inc. a...@redhat.com -----------------------------------
