Messages in this thread | | | From | Jim Mattson <> | Date | Fri, 24 Apr 2020 09:25:06 -0700 | Subject | Re: [PATCH] [RFC] kvm: x86: emulate APERF/MPERF registers |
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On Fri, Apr 24, 2020 at 7:46 AM Sean Christopherson <sean.j.christopherson@intel.com> wrote: > > On Fri, Apr 24, 2020 at 12:01:43PM +0200, Peter Zijlstra wrote: > > On Fri, Apr 24, 2020 at 01:08:55PM +0800, Li RongQing wrote:
> This requires four RDMSRs per VMX transition. Doing that unconditionally > will drastically impact performance. Not to mention that reading the MSRs > without checking for host support will generate #GPs and WARNs on hardware > without APERFMPERF. > > Assuming we're going forward with this, at an absolute minimum the RDMSRs > need to be wrapped with checks on host _and_ guest support for the emulated > behavior. Given the significant overhead, this might even be something > that should require an extra opt-in from userspace to enable.
I would like to see performance data before enabling this unconditionally.
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