> -----邮件原件----- > 发件人: Xu, Like [mailto:[email protected]] > 发送时间: 2020年6月5日 10:32 > 收件人: Li,Rongqing <[email protected]> > 抄送: [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected]; [email protected]; [email protected]; > [email protected] > 主题: Re: [PATCH][v6] KVM: X86: support APERF/MPERF registers > > Hi RongQing, > > On 2020/6/5 9:44, Li RongQing wrote: > > Guest kernel reports a fixed cpu frequency in /proc/cpuinfo, this is > > confused to user when turbo is enable, and aperf/mperf can be used to > > show current cpu frequency after 7d5905dc14a > > "(x86 / CPU: Always show current CPU frequency in /proc/cpuinfo)" > > so guest should support aperf/mperf capability > > > > This patch implements aperf/mperf by three mode: none, software > > emulation, and pass-through > > > > None: default mode, guest does not support aperf/mperf > s/None/Note > > > > Software emulation: the period of aperf/mperf in guest mode are > > accumulated as emulated value > > > > Pass-though: it is only suitable for KVM_HINTS_REALTIME, Because that > > hint guarantees we have a 1:1 vCPU:CPU binding and guaranteed no > > over-commit. > The flag "KVM_HINTS_REALTIME 0" (in the Documentation/virt/kvm/cpuid.rst) > is claimed as "guest checks this feature bit to determine that vCPUs are never > preempted for an unlimited time allowing optimizations". > > I couldn't see its relationship with "1:1 vCPU: pCPU binding". > The patch doesn't check this flag as well for your pass-through purpose. > > Thanks, > Like Xu
I think this is user space jobs to bind HINT_REALTIME and mperf passthrough, KVM just do what userspace wants. and this gives user space a possibility, guest has passthrough mperfaperf without HINT_REALTIME, guest can get coarse cpu frequency without performance effect if guest can endure error frequency occasionally -Li
