On Thu, 2019-10-03 at 20:05 +0200, Rafael J. Wysocki wrote: > On Wednesday, October 2, 2019 2:29:26 PM CEST Giovanni Gherdovich > wrote: > > From: Srinivas Pandruvada <srinivas.pandruv...@linux.intel.com> > > > > 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 > > readas well > > any APERF/MPERF MSRs. > > Well, this isn't quite convincing. > > In particular, I don't see why the "don't read APERF/MPERF MSRs" > argument > applies *only* to intel_pstate in the "active" mode. What about > intel_pstate > in the "passive" mode combined with the "performance" governor? Or > any other > governor different from "schedutil" for that matter? > > And what about acpi_cpufreq combined with any governor different from > "schedutil"? > > Scale invariance is not really needed in all of those cases right now > AFAICS, > or is it? Correct. This is just part of the patch to disable in active mode (particularly in HWP and performance mode).
But this patch is 2 years old. The folks who wanted this, disable intel-pstate and use userspace governor with acpi-cpufreq. So may be better to address those cases too. > > So is the real concern that intel_pstate in the "active" mode reads > the MPERF > and APERF MSRs by itself and that kind of duplicates what the scale > invariance > code does and is redundant etc? It is redundant in non-HWP mode. In HWP and performance (active mode) we don't use atleast at this time. Thanks Srinivas
