On Wed, May 16, 2018 at 9:29 AM, Peter Zijlstra <pet...@infradead.org> wrote: > On Wed, May 16, 2018 at 09:16:40AM +0200, Peter Zijlstra wrote: >> 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? > > Bah, I cannot read it seems. active is when we use the intel_pstate > governor and passive is when we use schedutil and only use intel_pstate > as a driver. > >> 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? > > That still stands.. this needs to be properly explained.
I guess this is from the intel_pstate perspective only. The active mode is only used with HWP, so intel_pstate doesn't look at the utilization (in any form) in the passive mode today. Still, there are other reasons for PELT to be scale-invariant, so ...