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HWP vs "xenpm get-cpufreq-..."


  • To: Jason Andryuk <jandryuk@xxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Mon, 15 Jan 2024 17:04:39 +0100
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Mon, 15 Jan 2024 16:04:56 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

Jason,

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.

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?

Thanks, Jan



 


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