Re: [PATCH v2 2/3] KVM: X86: Provide a capability to disable cstate msr read intercepts

[Wanpeng Li]

On Tue, 11 Jun 2019 at 19:09, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
>
> On 11/06/19 09:38, Wanpeng Li wrote:
> > MSR_CORE_C1_RES is unreadable except for ATOM platform, so I think we
> > can avoid the complex logic to handle C1 now. :)
>
> I disagree.  Linux uses it on all platforms is available, and virtual
> machines that don't pass mwait through _only_ have C1, so it would be
> less useful to have deep C-state residency MSRs and not C1 residency.
>
> But turbostat can get the information from sysfs, so what are these MSRs
> used for?

The sysfs is not accurate, the time which is accumulated in the
function cpuidle_enter_state() is the expected cstate we hope to enter
instead of the real cstate we finally enter. For example, we found
several SKX/CLX models can't enter deeper cstates in non-root mode,
Intel hardware team has been working on this according to our report
recently. The bare-metal cstate residency msrs don't increase in
non-root mode, however, the time under
/sys/devices/system/cpu/cpux/cpuidle/statex/ increase gradually in the
guest.

Regards,
Wanpeng Li