On 04/21/2016 11:30 PM, Viresh Kumar wrote: > On 19-04-16, 16:12, Ashwin Chaugule wrote: >> + Ryan >> >> Hi Al, >> >> On 18 April 2016 at 20:11, Al Stone <ahs3@xxxxxxxxxx> 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). >>> >>> While the investigation for a long term fix proceeds (several options >>> are being explored, some of which may require spec changes or other >>> much more invasive fixes), this patch forces the values read by CPPC >>> to be read in KHz, regardless of what they actually represent. >>> >>> 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. This >>> patch retrieves the first 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. > > Don't we have any big LITTLE ARM servers yet ? Or we will not have them at all ? My apologies, but I missed this question earlier and just now noticed it. AFAIK, there are no big.LITTLE ARM servers yet. That doesn't mean there aren't any, or that no one is planning one; I just don't know of any. I have been in discussions about doing that, but in the past those have ended up concluding that there is probably no need for that level of power management in a server. -- ciao, al ----------------------------------- Al Stone Software Engineer Red Hat, Inc. ahs3@xxxxxxxxxx ----------------------------------- -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
