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Re: [PATCH v2 0/4] arm64: Add the cpufreq device to show cpufreq info to

From: Andrew Jones
Subject: Re: [PATCH v2 0/4] arm64: Add the cpufreq device to show cpufreq info to guest
Date: Thu, 13 Feb 2020 09:18:54 +0100

On Thu, Feb 13, 2020 at 03:36:26PM +0800, Ying Fang wrote:
> On ARM64 platform, cpu frequency is retrieved via ACPI CPPC.
> A virtual cpufreq device based on ACPI CPPC is created to
> present cpu frequency info to the guest.
> The default frequency is set to host cpu nominal frequency,
> which is obtained from the host CPPC sysfs. Other performance
> data are set to the same value, since we don't support guest
> performance scaling here.
> Performance counters are also not emulated and they simply
> return 1 if read, and guest should fallback to use desired
> performance value as the current performance.
> Guest kernel version above 4.18 is required to make it work.

This is v2 of the series, but I don't see a changelog.

Can you please describe the motivation for this? If I understand
correctly, all of this is just to inform the guest of the host's
CPU0 nominal or max (if nominal isn't present?) frequency. Why
do that? What happens if the guest migrates somewhere where the
frequency is different? If this is for a special use case, then
why not come up with a different channel (guest agent?) to pass
this information?


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