Re: [RFC/RFT] [PATCH 02/10] cpufreq: intel_pstate: Conditional frequency invariant accounting

[Peter Zijlstra]

On Tue, May 15, 2018 at 09:49:03PM -0700, Srinivas Pandruvada wrote:
> intel_pstate has two operating modes: active and passive. In "active"
> mode, the in-built scaling governor is used and in "passive" mode,
> the driver can be used with any governor like "schedutil". In "active"
> mode the utilization values from schedutil is not used and there is
> a requirement from high performance computing use cases, not to read
> any APERF/MPERF MSRs. In this case no need to use CPU cycles for
> frequency invariant accounting by reading APERF/MPERF MSRs.
> With this change frequency invariant account is only enabled in
> "passive" mode.

WTH is active/passive? Is passive when we select performance governor?

Also; you have to explain why using APERF/MPERF is bad in that case. Why
do they care if we read those MSRs during the tick?