Re: [PATCH v5 3/3] Add support for RAPL MSRs in KVM/Qemu

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Apr 17, 2024 at 06:07:02PM +0800, Zhao Liu wrote:
> Hi Anthony,
> 
> May I ask what your usage scenario is? Is it to measure Guest's energy
> consumption and to charged per watt consumed? ;-)
> 
> On Thu, Apr 11, 2024 at 02:14:34PM +0200, Anthony Harivel wrote:
> > Date: Thu, 11 Apr 2024 14:14:34 +0200
> > From: Anthony Harivel <aharivel@redhat.com>
> > Subject: [PATCH v5 3/3] Add support for RAPL MSRs in KVM/Qemu
> > 
> > Starting with the "Sandy Bridge" generation, Intel CPUs provide a RAPL
> > interface (Running Average Power Limit) for advertising the accumulated
> > energy consumption of various power domains (e.g. CPU packages, DRAM,
> > etc.).
> >
> > The consumption is reported via MSRs (model specific registers) like
> > MSR_PKG_ENERGY_STATUS for the CPU package power domain. These MSRs are
> > 64 bits registers that represent the accumulated energy consumption in
> > micro Joules. They are updated by microcode every ~1ms.
> 
> What is your current target platform?

I think we can assume /all/ future CPUs are conceptially in scope
for this.

The use case is to allow guest owners to monitor the power consumption
of their workloads, so they can take steps to optimize their guest VM
workloads to reduce power consumed.

> On future Xeon platforms (EMR and beyond) RAPL will support TPMI (an MMIO
> interface) and the TPMI based RAPL will be preferred in the future as
> well:

Is the MSR based interface likely to be removed in future silicon,
or it will be remain for back compat ?

> * TPMI doc: https://github.com/intel/tpmi_power_management
> * TPMI based RAPL driver: drivers/powercap/intel_rapl_tpmi.c
> 

With regards,
Daniel
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