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

[Marcelo Tosatti <mtosatti@redhat.com>]

On Fri, Jun 16, 2023 at 04:08:30PM +0200, Anthony Harivel wrote:
> 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.
> 
> For now, KVM always returns 0 when the guest requests the value of
> these MSRs. Use the KVM MSR filtering mechanism to allow QEMU handle
> these MSRs dynamically in userspace.
> 
> To limit the amount of system calls for every MSR call, create a new
> thread in QEMU that updates the "virtual" MSR values asynchronously.
> 
> Each vCPU has its own vMSR to reflect the independence of vCPUs. The
> thread updates the vMSR values with the ratio of energy consumed of
> the whole physical CPU package the vCPU thread runs on and the
> thread's utime and stime values.
> 
> All other non-vCPU threads are also taken into account. Their energy
> consumption is evenly distributed among all vCPUs threads running on
> the same physical CPU package.
> 
> This feature is activated with -accel kvm,rapl=true.

I suppose this should be a CPU flag instead? -cpu xxx,rapl=on.