On 15.01.2024 17:45, Jason Andryuk wrote: > On Mon, Jan 15, 2024 at 11:04 AM Jan Beulich <[email protected]> wrote: >> I thought I'd try hwp on a SapphireRapids system, and of course - short >> of easy other ways of seeing whether it actually has any apparent >> effect - I've looked at "xenpm get-cpufreq-states" output. Just to find >> that according to this, the system never enters any of the designated >> Pn states (all CPUs are always claimed to be in P0), while at the same >> time the P0 residencies remain in the hundreds of milliseconds. The >> latter suggests CPUs do leave P0, yet it's then unclear what state they >> are in during such time periods. > > The `xenpm get-cpufreq-states` output may be stale under HWP. If > normally the acpi-cpufreq driver is updating them, they won't be > updated under HWP. I'll have to look into that more, but I guess they > shouldn't be returned under HWP.
Likely - anything that conveys no real information (and hence is at best confusing) would better be avoided. >> I was also a little puzzled when comparing "xenpm get-cpufreq-para" >> output with hwp against that with acpi-cpufreq: The latter lists a range >> of 800MHz ... 2501MHz, while with hwp base is 2500MHz and max is 4800MHz. >> >> Do you have any explanation for these apparent anomalies? > > The 1 in 2501 indicates the ACPI entry for the turbo frequencies. > It's a limitation of the ACPI tables, AFAIU. The tables weren't > designed for turbo mode where the thermal constraints dynamically > limit the maximum speed. On systems I've looked at, there would also > be a 2500MHz ACPI entry, which matches the HWP base. > > The HWP 2500MHz & 4800MHz values are taken from cpuid output - I feel > confident they are correct. The output of `xenpm get-cpufreq-average` > under HWP looks reasonable for scaling all the way up to 4800MHz > (which can only be hit briefly before throttling down) - I think I've > only seen ~4700MHz as a maximum in my use, and they it may drop to > ~4200MHz for extended preiods. Maybe try that command on your test > system? I'll try to remember to check that next time round. Jan
