Re: [PATCH v3] perf/rapl: support per domain energy unit

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Mon, 15 Jun 2015 13:32:01 -0400 (EDT)
Vince Weaver <vincent.weaver@maine.edu> wrote:

> On Thu, 26 Mar 2015, Jacob Pan wrote:
> 
> > RAPL energy hardware unit can vary within a single CPU package, e.g.
> > HSW server DRAM has a fixed energy unit of 15.3 uJ (2^-16) whereas
> > the unit on other domains can be enumerated from power unit MSR.
> > There might be other variations in the future, this patch adds
> > per cpu model quirk to allow special handling of certain cpus.
> 
> So I have a Desktop Haswell machine (model 60) that is instrumented
> to measure actual DRAM power at the DIMM (with a sense resistor).
> 
> We are consistently getting RAPL results roughly a factor of 2
> smaller than the actual, measured results.
> 
> Does desktop Haswell have a similar units issue to Haswell-EP?
> 
Not that I know of. perhaps has to do with the difference of what
and where we are measuring. Let me find a instrumented system to verify
and get back to you.
> I wasted a bunch of time trying to decode the 
> DRAM_ENERGY_SCALEFACTOR_MCHBAR values described in the
> Desktop 4th Generation Intel Core Processor Family
> datasheet but possibly that value in the MCHBAR is unrelated to the
> one exported by the RAPL interface.
> 
This scale factor is not directly related to the energy counter. The
MMIO DRAM RAPL energy status uses the same unit as the MSR interface,
the resolution is ~61uJ.

> Vince

[Jacob Pan]